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THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 

MRS.  PRUDENCE  W.  KOFOID 


Dunglisori }s  American  Medical  Library. 


THE 


STUDENT'S  COMPENDIUM 


OF 


COMPARATIVE  ANATOMY. 


BY  P.  EYERS, 

LICENTIATE  OF  THE  ROYAL  COLLEGE  OF  SURGEONS  IN  IRELAND,  &C. 


Sparsa  coegi."— Ovid. 


PHILADELPHIA : 

PRINTED  AND  PUBLISHED  BY  A.  WALDIE,  40  CARPENTER  ST. 

1839. 


TO 

PHILIP  CRAMPTON,  M.  D.,  F.  R.  S. 

SURGEON   GENERAL    TO   THE    FORCES    IN    IRELAND, 

<fcc.  Sec.  Sec. 

AS    AN    INADEQUATE,  BUT    SINCERE    TESTIMONY    OF    RESPECT, 

TO 

DISTINGUISHED    SCIENTIFIC    ATTAINMENTS, 

AND 

DESERVED    PROFESSIONAL    EMINENCE, 

THIS   VOLUME 

IS   INSCRIBED, 

BY 

HIS    GRATEFUL    AND    OBLIGED    FRIEND, 

THE  AUTHOR. 


y&w 


PREFACE. 


In  the  compilation  of  these  pages  no  originality  is  claimed,  but 
the  labours  of  modern  authors  have  been  freely  appealed  to,  and 
it  is  trusted,  on  every  occasion,  with  due  respect.  A  list  of  the 
several  authors  consulted  has  been  added  at  the  end  of  the  book. 

I  have  to  acknowledge  several  obligations  to  my  friend  Dr. 
Houston  of  this  city,  whose  scientific  acquirements  and  connec- 
tion with  the  Museum  of  the  College,  have  well  qualified  him  for 
the  many  auxiliary  favours  he  has  conferred  on  me. 

P.  E. 

Dublin,  33  Aungier  Street, 
September,  1838. 


COMPENDIUM 


OF 


COMPARATIVE    ANATOMY. 


CHAPTER  I. 

PRELIMINARY  OBSERVATIONS. 

When  we  turn  our  attention  to  the  busy  theatre  of  animal  life, 
we  are  at  once  attracted  by  scenes  of  wonder  and  delight.  The 
works  of  nature  appear  unbounded  in  extent,  variety,  and  riches. 
Wherever  the  eye  is  cast,  from  the  icy  regions  of  the  pole  to  the 
scorching  sands  of  the  line,  it  beholds  life  displayed  in  forms  as 
endless  as  they  are  enchanting. 

Every  region  and  every  element  is  the  abode  of  numerous  animals, 
and  is  admirably  suited  to  their  peculiar  living  habits  and  instincts  ; 
the  vastness  of  their  number  may  be  estimated  from  the  declaration 
of  the  celebrated  Ehrenberg,  that  a  single  cubic  line  which  is  less 
than  a  drop  of  fluid  contains  500,000,000  monads. 

But  however  varied  and  delightful  the  occupations  of  the  zoolo- 
gist may  be,  his  information  is  still  defective,  and  he  perceives  that 
the  interior  machinery  of  life  is  hidden  from  his  observation,  and  its 
springs  concealed  by  clouds  which  nothing  but  the  light  of  dissec- 
tions can  dispel. 

When  once  engaged  in  this  captivating  department  of  his  inves- 
tigations, he  begins  to  observe  the  beautifully  progressive  develop- 
ment of  organisation,  varied  and  modified  in  obedience  to  certain 
laws ;  he  will  often  behold  the  same  animal,  according  to  the  parti- 
cular epoch  of  its  existence,  undergoing  metamorphosis,  appearing 
under  different  characters,  and  playing  very  different  parts  on  the 
stage  of  life. 

Having  entered  a  little  more  fully  into  the  details  of  comparative 
anatomy,  he  will  often  observe  an  organ  which  has  attained  a  high 
degree  of  development,  and  whose  functions  are  perfectly  under- 
stood in  one  animal ;  diminutive,  rudimentary,  and  apparently  use- 
less in  another.  Hence  it  must  be  obvious,  that  he  who  aspires  to  a 
perfect  knowledge  of  human  structure  and  function,  must  extend 
his  researches  to  an  examination  of  the  animal  kingdom  in  general ; 
and  accordingly  great  advantage  will  be  found  in  a  previous  ac- 
quaintance with  some  one  or  more  of  the  most  approved  classifica- 
tions in  natural  history. 

Every  classification  hitherto  proposed  has  in  some  particular  or 
other  its  imperfections  ;  but  it  matters  little  what  scale  we  adopt. 


8  EVERS'S  COMPARATIVE  ANATOMY. 

or  whether  we  make  use  of  several,  provided  that  our  object  of  con- 
veying or  acquiring  a  knowledge  of  the  comparative  structure  of 
animal  bodies  be  attained.  This  must  be  my  excuse  for  appearing 
in  some  places  to  have  followed  the  arrangement  of  Cuvier,  and  in 
others,  that  of  Dr.  Grant,  both  having  their  excellences,  and  their 
authors  holding  the  highest  place  as  authorities  on  the  subject. 

Cuvier's  and  Grant's  classifications  are  therefore  subjoined,  ac- 
companied by  familiar  illustrations  of  each,  to  lead  the  student  at 
one  glance  to  the  objects  which  each  subdivision  embraces.  The 
examples  appended  to  Grant's  classification  have  been  added  by 
myself,  whilst  those  of  Cuvier  have  been  taken  from  Dr.  Houston's 
Descriptive  Catalogue  of  the  Preparations  in  the  Museum  of  the 
Royal  College  of  Surgeons  in  Ireland,  with  a  few  additional  exam- 
ples from  Roget's  Bridgewater  Treatise. 

It  might  appear  an  omission  not  to  make  some  allusion  to  the 
arrangement  of  the  animal  kingdom  adopted  by  the  immortal  Lin- 
neeus,  but  the  researches  of  later  zoologists  have  proved  it  so  defec- 
tive, that  it  is  not  followed  by  any  writer  or  teacher  of  the  present 
day,  and  needs  therefore  but  a  cursory  allusion.  Suffice  it  to  state 
that  he  divided  the  whole  animal  kingdom  into  six  classes,  Mam- 
malia, Aves,  Reptilia,  Pisces,  Insecta,  Vermes,  founding  his  classi- 
fication mainly  on  the  peculiarities  afforded  by  the  respiratory  and 
sanguineous  systems. 


OUTLINE  OF  CUVIER'S  CLASSIFICATION  OF  ANIMALS. 

FOUR  GREAT  DIVISIONS. 

1.  Vertebrata.  3.  Articulata. 

2.  Mollusca.  4.  Radiata. 

VERTEBRATA. 

Characters. — Internal  skeleton — brain  and  spinal  marrow  in  separate  cavi- 
ties— red  blood  and  muscular  heart — mouth  with  horizontal  jaws — five 
organs  of  sense — never  more  than  four  limbs — separate  sexes. 

MOLLUSCA. 

Ch. — No  skeleton — muscles  all  attached  to  external  skin — nervous  system 
situated  in  the  visceral  cavity  and  composed  of  separate  masses  joined  by 
nervous  filaments — taste,  sight,  or  as  in  one  instance,  hearing,  the  only  senses 
— organs  of  circulation,  respiration,  and  digestion  very  perfect. 

ARTICULATA. 

Ch. — No  skeleton — two  long  nervous  chords  with  ganglia  at  intervals — 
have  usually  taste  and  sight — divided  in  jointed  rings,  soft  or  hard,  to  inside 
of  which  muscles  attached — sometimes  lateral  limbs,  sometimes  none — jaws 
when  present  alwavs  lateral. 


CLASSIFICATION. 


RADIATA. 


Ch. — Organs  of  movement  and  sense  disposed  circularly  around  a  centre, 
not  symmetrically  as  in  the  preceding — no  visible  nerves — no  organs  of  sense 
or  circulation — respiration  by  the  outward  integument — intestines  often  a 
simple  bag— sometimes  the  animal  is  but  a  homogeneous  pulp  without  aper- 
ture or  cavity. 


I.  YERTEBRATA. 

Class  1.  MAMMALIA. 
Order  1.  Bimana      -    -   Examples,  Man. 


2.  q,cadrumana 

3.  Cheirotera    - 

4.  Insectivora    - 

5.  Plantigrada  - 

6.  DlGITIGRADA      - 

7.  Amphibia    -    - 

8.  Marsdpialia  - 

9.  Edentata  -    - 

10.  Rodentia  -    - 

11.  ruminantia    - 

12.  Pachydermata 

13.  Cetacea 


Cl.  2.  AVES. 


Orel 


Exam. 


Orel 


Orel. 


1.  Accipitres 

2.  Passeres    -     -       

3.  ScANSORES  -      -  

4.  GALLIN2B      -      -  

5.  Grallje       -     -       

6.  Palmipedes     -        

Cl.  3.  REPTILIA. 

1.  Chelonia  -  Exam. 

2.  Sauria   -   -  -  

3.  Ophidia      -  -  

4.  Batrachia  -  

Cl.  4.  PISCES. 
1.  Chondropterygii  Exam. 


Monkey,  ape,  lemur. 

Bat,  colugo. 

Hedge-hog,  shrew,  mole. 

Bear,  badger,  glutton. 

Dog,  lion,  cat,  marten,  weasel,  otter, 

Seal,  walrus. 

Opossum,  kangaroo,  wombat. 

Sloth,  armadillo,  ant-eater. 

Beaver,  rat,  squirrel,  porcupine,  hare, 

Camel,  deer,  giraffe,  sheep,  ox. 

Elephant,  hog,  rhinoceros,  tapir,  horse, 

Dolphin,  whale. 


Vulture,  eagle,  owl,  hawk. 
Thrush,  swallow,  lark,  crow,  sparrow. 
Woodpecker,  cuckoo,  toucan,  parrot. 
Peacock,  pheasant,  grouse,  pigeon. 
Plover,  stork,  snipe,  ibis,  flamingo. 
Auk,  grebe,  gull,  pelican,  swan,  duck. 


Tortoise,  turtle,  emys. 

Crocodile,  lizard,  gecko,  chameleon. 

Serpents,  boa,  viper. 

Frog,  salamander,  newt,  proteus,  siren, 


2.  Malacopterygii 

3.  LoPHOBRANCHII 

4.  Pleclognatiii 

5.  Acanthopterygii 


Head  crowned  with  tenta- 
cula  which  serve  as  feet 

Progression  by  fins  placed 
near  the  head. 

Head  free  progression  on 
the  belly. 

Without  distinct  head. 


:■ 


Lamprey,  shark,  ray,  sturgeon. 
Salmon,  herring,  cod,  sole,  eel. 

Pike-fish,  pegasus. 

Sun-fish,  trunk-fish. 

Perch,  mackerel,  sword-fish. 

II.  MOLLUSCA. 
Cl 


I.  Cephalopoda  Exam.  Cuttle-fish,  cala- 
mary,  nautilus. 


2.  Pteropoda 

3.  Gasteropoda 

4.  Acephala 


Clio,  hyaloea. 

Slug,  snail,  lim- 
pet. 

Oyster,  muscle, 
ascidia. 


10 


EVERS  S  COMPARATIVE  ANATOMY. 


Two  long  arms  at  the  mouth 
for  seizing  objects. 

Arms  very  numerous,  arti- 
culated, horny. 


5.  Brachiopoda  Exam.  Lingula,  tereba- 

tula. 

6.  Cirrhopoda     Barnacle,  triton. 


III.  ARTIOULATA. 
CI.  1.  ANNELIDA. 


Ord.  1.  Tubicola   -   -    - 

2.  Dorsibranchia  - 

3.  Abranchia    -    - 


-    Exam. 


Serpula,  sabella,  amphitrite. 
Nereis,  aphrodite,  lob-worm. 
Earth-worm,  leech,  nais,  hair-worm. 


Cl.  2.  CRUSTACEA. 

Ord.  1.  Malacostraca  -  -  Exam. 

2.  Decapoda      -    -  -    

3.  Stomopoda    -    -  -    

4.  Amphipoda    -     -  -     i 

5.  LiEMODIPODA  -      -      

6.  ISOPODA       -      -      -      -      , . 

7.  Entomostrata  -    -    

Cl.  3.  ARACHNIDA. 
Ord.  1.  Pulmonalia  -    -    -    Exam. 


2.  Trachealia 


Cl.  4.  INSECTA. 


Ord.  1.  Aptera    -    - 

2.  Coleoptera  - 

3.  Ortiioptera 

4.  Hemiptora  - 

5.  Neuroptera 

6.  Hymenoptera 

7.  Lepidoptera 

8.  Rhipiptera  - 

9.  Diptera  -    - 


Exam. 


Lobster,  crab,  prawn. 

Squill,  phyllosoma. 

Grammarus,  sand-hopper. 

Cyamus. 

Wood-louse. 

Monoculus. 


Spider,  tarantula,  scorpion. 
Phalangium,  mite. 


Centipede,  podura. 
Beetle,  glow-worm. 
Grass-hopper,  locust. 
Fire-fly,  aphis. 
Dragon-fly,  ephemera. 
Bee,  wasp,  ant. 
Butter-fly,  moth. 
Xenos,  stylops. 
Gnat,  house-fly. 


IV.  RADIATA  vel  Zoophyta. 


ClaSS  1.    ECHINODERMATA 

2.  Entozoa     -  - 

3.  acalephje  -  - 

4.  Polypi    - 

5.  Infusoria    -  - 


Exam.  Star-fish,  sea-urchin. 

! Fluke,  hydatid,  tape-worm. 

Actinia,  medusa. 

Hydra,  coral,  madrepore,  pennatula. 

Brachionus,  vibrio,  proteus,  monas. 


GRANT'S  DIVISION  OF  THE  ANIMAL  KINGDOM. 

Division.  Class. 


f     1.    POLYASTRICA 

I.  CYCLO-NEURAl   I  £°RIFE*A    "    " 

-RAD.ATA      1    4:I0orEP„T-    I 
I  5.  Echinodermata 


Exam.  Monad,  madrepore. 

— Sponges. 

Polypes,  corals. 

Medusa,  actinia. 


Star-fish,  sea-urchin. 


SKELETON  IN  THE  INVERTEBRATA. 


11 


Division. 


II.  DIPLO-NEURA 
vel  ARTICULA- 
TA. 


III.  CYCLO-GAN- 
GLIATA   vel 
MOLLUSCA. 


IV.   SPINI-CERE- 
BRATA  vel 
VERTEBRATA. 


Class. 
f  6.  Entozoa    - 


7. 
8. 
9. 
10. 
11. 
12. 
113. 
fl4. 
115. 
{jft. 
117. 

Lis. 
f19. 

I  20. 
<2l. 

|  22. 
123. 


Rotifera    - 

ClRRHOPODA 
ANiNELIDA     - 

Myriapoda 
Insecta -     - 
Arachnida 
Crustacea 
Tdnicata   - 
conchifera 
Gasteropoda 
Pteropoda 
Cephalopoda 
Pisces    -    - 
Amphibia    - 
Reptilia     - 
Aves       -     - 
Mammalia 


Exam.  Intestinal  worms,  hyda- 
tids. 

Patella. 

Barnacle,  triton. 

Earth-worm,  leech, 

Scolopendra. 

Bee,  butter-fly. 

Spider,  scorpion. 

Lobster,  crab. 

Ascidia  intestinalis. 

Muscle,  oyster. 

Slug,  snail. 

■ Clio,  hvalosa. 

Cuttle-fish. 

Salmon,  shark,  eel. 

Frog,  toad,  proteus. 

Tortoise,  lizard,  serpent. 

1 Eagle,  heron,  duck. 

Man,  kangaroo,  whale. 


Many  other  arrangements  of  the  animal  kingdom  have  been  pro- 
posed by  different  zoologists;  some,  as  Linneeus,  founding  their  basis 
of  classification  on  the  vascular  and  respiratory  systems,  and  others  on 
the  peculiarities  afforded  by  the  generative  organs.  Aristotle  divided 
all  animals  into  those  with,  and  those  without  red  blood;  and 
Lamark  into  the  apathic,  the  sensitive,  and  the  intelligent. 


CHAPTER  II. 


SKELETON  IN  THE  INVERTEBRATA. 

General  observations. — The  skeleton  gives  figure,  strength,  and 
solidity  to  the  entire  frame ;  it  serves  as  a  basis  of  support  to  the 
soft  parts,  forms  levers  of  locomotion,  and  encloses  cavities  to  pro- 
tect and  defend  the  most  delicate  and  important  organs.  Its  use, 
however,  being  chiefly  of  a  mechanical  nature,  it  will  be  found  to 
vary  much,  according  to  the  respective  wants,  habits,  and  instincts 
of  animals.  In  all  the  operations  of  nature  we  find  that  there  is  a 
rigid  economy  observed ;  the  means  employed  are  such  only  as 
are  required,  and  always  the  most  simple  by  which  the  intended 
purposes  can  be  accomplished.  Hence  we  shall  not  be  surprised  to 
meet  with  infinitely  varied  modifications  of  skeleton  throughout 
the  widely  extended  range  of  the  animal  world.  The  chemical 
composition  of  this  solid  frame-work  presents  some  variety.  For 
instance,  silica  is  found  in  the  lowest  forms  of  the  radiata ;  carbo- 
nate of  lime  in  the  molluscous  animals;  carbonate  and  phosphate  of 
lime  in  the  articulata ;  and  phosphate  of  lime  in  the  organised  skele- 
tons of  the  vetebrata.  This  frame-work  is  sometimes  placed  external 
to  the  soft  parts,  and  in  others  it  is  internal  to  them.  In  no  instance 
do  we  meet  with  a  bony  skeleton  except  in  animals  possessed  of 


12 

a  regularly  formed  brain  ;  and  here  it  is  obvious  to  those  who  un- 
derstand the  difference  between  the  growth  of  shell  and  bone  that 
the  former  would  be  unfit  for  the  purpose,  since  there  is  no  provi- 
sion made  for  the  enlargement  of  the  original  cavity. 

Radiata,  Cuvier  ;  Cyclo-neura,  Grant. — In  this  acrite  or 
lowest  division  of  the  animal  kingdom  the  skeleton  generally  holds 
an  internal  situation,  and  is  composed  either  of  one  large  mass  or 
several  smaller  pieces  symmetrically  disposed,  composed  of  silicious 
or  calcareous  spicula.  In  many  of  the  polygastrics  the  organ  of 
support  consists  in  a  condensation  of  the  common  integument  en- 
veloping the  body — occasionally  in  the  form. of  an  elastic  vagini- 
form  sheath  into  which  the  animal  can  retreat  on  the  approach  of 
danger,  (fee,  as  seen  in  the  vaginicola  innata.  Among  the  pori- 
phera,  skeletons  are  met  with  of  a  horny,  silicious,  or  calcareous 
structure,  variously  modified.  In  none  does  nature  seem  to  have 
amused  herself  more  in  the  construction  of  skeletons  than  among  the 
zoophytes.  Here  they  are  met  with  internal  or  external,  soft,  horny, 
or  calcareous  ;  branched,  globular,  or  filiform  ;  free  or  fixed.  The 
astenas  and  others  of  the  echinodermata  present  us  with  skeletons 
in  the  form  of  external  crusts  or  shells,  disposed  after  the  manner 
of  plates,  and  composed  of  carbonate,  with  a  trace  of  phosphate 
of  lime. 

Articidata,  Cuvier;  Diplo-nerose  Animals,  Grant. — The  bo- 
dies of  these  animals  are  generally  long,  cylindrical,  and  divided 
transversely  into  segments.  Their  skeletons  are  generally  thin, 
light,  and  situate  externally,  chiefly  composed  of  phosphate  of  lime, 
though  occasionally  of  carbonate,  as  in  the  cirrhopoda  and  Crusta- 
cea. The  entozoa  owe  their  peculiar  stiffness  and  rigidity  to  the 
tough,  strong,  and  transparent  covering  enveloping  their  entire 
body.  In  some  of  the  inferior  orders  of  them,  as  in  the  acanthoce- 
phalous  species,  their  retractile  proboscis  and  part  of  their  bodies 
are  set  with  dense,  sharp  spines,  which  enable  them  to  move  with 
freedom  and  precision  through  the  fleshy  media  in  contact  with 
them.  The  rotifera  are  closely  allied  to  the  entozoa  in  their  ex- 
terior coverings.  In  the  former,  however,  this  texture  possesses  a 
greater  degree  of  firmness,  from  the  attachment  of  numerous  mus- 
cles to  it.  There  are  no  earthy  deposits  in  any  part  of  the  body  of 
these  animals.  The  cirrhopoda,  like  the  mollusca,  are  usually 
enclosed  in  shells,  dense,  thin,  laminated,  and  composed  of  carbo- 
nate of  lime.  These  testaceous  coverings  are  best  developed  in  the 
balani.  and  least  in  the  anatiferse.  The  reverse  order  of  develop- 
ment obtains  with  respect  to  their  extremities. 

The  amielida,  or  red-blooded  worms,  lead  us  a  step  higher  in 
the  development  of  skeleton;  for,  although  the  halithea,  the  leech, 
the  nais,  &c,  possess  a  flexible  membraneous  covering,  many  others, 
as  the  serpulas,  are  shielded  by  adventitious,  solid,  calcareous  tubes. 
The  common  earth-worm  is  provided  with  four  pairs  of  sharp 
spines,  or  setas,  for  the  purpose  of  progression.  The  skeleton  of 
insects  is  for  the  greater  part  composed  of  a  thin,  epidermic  layer, 


SKELETON  IN  THE  INVERTEBRATA.  l3 

and  a  thick  internal  one  resembling  the  woody  fibres  of  plants,  but 
of  an  animal  nature,  termed  chitine  and  coccine,  blended  with  por- 
tions of  phosphate  of  lime,  magnesia  and  iron.  These  animals 
also  present  distinct  legs  and  wings. 

In  the  arachnida  we  meet  with  a  more  consolidated  form  of 
skeleton;  generally  more  than  three  pairs  of  legs  :  and,  at  the  sides 
of  their  head,  a  pair  of  sharp-pointed  piercing" instruments,  suited 
to  their  retired,  cunning,  and  carnivorous  habits.  These  animals 
throw  off  periodically  their  exterior  coverings,  like  the  larvae  of 
insects;  and,  like  the  Crustacea,  they  are  capable  of  reproducing 
their  members  when  destroyed.  The  Crustacea  affords  us  by  far 
the  most  solid  form  of  skeleton  met  with  in  any  of  the  articulata. 
In  the  decapods  it  contains  half  its  weight  of  carbonate  of  lime, 
and  a  considerable  proportion  of  phosphate,  with  traces  of  iron, 
soda,  and  magnesia,  all  of  which  are  secreted  from  the  true  skin. 
These  animals  have  generally  five  pairs  of  legs,  two  strong  mandi- 
bles, two  pairs  of  slender  maxillae,  and  two  pairs  of  antennae.  The 
solid  crust  forming  the  skeleton  of  Crustacea  is  cast  off  periodically. 
This  is  accomplished  by  the  animal  first  detaching  the  cutis  and 
muscles  from  the  inner  surface  of  the  old  shell;  "then  secreting 
from  the  surface  of  the  cutis  a  new  layer  of  epidermis ;  next  a  layer 
of  colouring  matter;  and,  within  this,  the  calcareous  materials  of 
the  new  shell. 

Mollusca,  Cuvier  ;   Cyclo-gangliated  animals,  Grant.     The 
shells  of  these  animals  are  formed  of  carbonate  of  lime,  without 
the  phosphate,  and  are  remarkable  for  their  want  of  symmetry  on 
the  two  sides  of  the  body,  and  their  inconstancy  in  animals  of  simi- 
lar structure.     In  the  tunicata  we  meet  with  an  exterior  cartilagi- 
nous skeleton,  in  some  instances  thick  and  opaque,  as  in  the  ascidia 
— in  others  more  delicate  and  transparent,  as  in  the  cynthia  papil- 
lata.     The  shells  of  the  conchifera  usually  consist  of  two  movable 
pieces  placed  on  the  exterior  of  the  body,  connected  by  ligament 
and  muscle.     All  these  animals,  however,  are  not  bivalved  ;  some, 
as  the  pholades,  have  additional  pieces  at  the  hinge  of  the  valve, 
constituting  the  multivalves.     They  have  a  muscular  foot,  and  a 
pair  of  tentacula.     The  gasterpoda  possess  hollow,  unilocular,  co- 
nical  shells.     Many  of  them   have  no  shell,  as  the  tritonia  and 
doris;  some  have  a  thin  calcareous  lamina  within  the  skin  of  the 
back,  as  the  aplysia;  whilst  others  have  only  a  partial  covering  of 
shell  as  the  testacella.     In  the  cephalopodous  mollusca  we  recog- 
nise the  transition  from  the  external  unorganised  shells  of  the  in- 
vertebrated  tribes  to  the  internal  organised  bones  of  the  vertebrata. 
The  shells  are  sometimes  external,  as  in  the  nautilus,  and  some- 
times internal,  as  in  the  sepia.     In  this  complicated  class  of  ani- 
mals we  find  a  near  approach  to  the  cartilaginous  fishes  in  the  pre- 
sence of  cranium,  spinal  column,  &c,  in  a  mdimental  form. 


14 


RECAPITULATION. 

1.  All  animals  are  included  under  the  heads  vertebrata  and  in- 
vertebrata. 

2.  Great  advantage  to  be  derived  from  a  knowledge  of  arrange- 
ment and  classification. 

3.  The  osseous  system  is  neither  the  most  important  nor  the 
most  uniformly  existing. 

4.  Skeleton  exists  in  every  class  of  animals,  but  modified  accord- 
ing to  each  class. 

5.  Skeleton  generally  internal  in  the  radiata,  and  external  in  the 
articulata,  subject  to  exceptions. 

6.  Skeleton  remarkable  for  inconstancy  and  want  of  symmetry 
in  the  mollusca. 

7.  Basis  of  skeleton — silica  in  the  lowest  radiata,  carbonate  and 
phosphate  of  lime  in  the  articulata,  and  carbonate  of  lime  chiefly  in 
the  mollusca. 

8.  No  bony  skeleton  where  regularly  formed  brain  does  not 
exist. 


CHAPTER  III. 

VERTEBRATA. 

General  observations. — It  will  appear  hereafter  that  the  principal 
part  of  the  nervous  system  consists  in  a  single  central  mass  extended 
along  the  back,  and  composed  of  a  series  of  distinct  portions,  each 
of  which,  like  the  cerebral  ganglion  of  one  of  the  sepiae,  is  indicated 
by  its  giving  off  one  or  more  pairs  of  nerves.  To  coincide  with  such 
a  disposition,  the  chief  portion  of  the  skeleton  is  formed  by  a  series 
of  osseous  rings,  which  being  mutually  articulated  and  collectively 
forming  a  closed  cavity,  compose  a  series  of  spinal  vertebra?  consti- 
tuting the  spinal  column — the  distinctive  character  of  this  division 
of  the  animal  sphere.  The  vertebral  column,  which  is  the  first 
rudiment  of  skeleton  observed  in  the  human  embryo,  is  also  the 
primary  and  most  essential  portion  of  it  in  the  higher  classes  of  ani- 
mals generally,  and  in  many  cases  alone  composes  nearly  the  whole 
of  the  skeleton. 

Another  characteristic  of  the  skeleton  in  this  department  of  ani- 
mals is,  that  it  is  placed  internal  to  the  soft  parts,  and  is  not  exuviable 
in  a  mass,  as  it  was  in  most  of  the  invertebrate  classes.  Here 
the  phosphate  of  lime  is  the  predominant  ingredient,  and  its  propor- 
tion increases  as  we  ascend  through  the  vertebrated  classes. 

The  appearance  of  the  skeleton  is  greatly  varied  by  the  situation 
of  the  ribs  ;  for  instance,  in  fish  and  aquatic  mammalia  the  thorax  is 
placed  near  the  anterior  part  of  the  column,  to  allow  of  the  mobility 


VERTEBRATA.  15 

of  the  posterior  portion  for  the  purposes  of  swimming.  In  birds, 
where  the  neck  is  used  as  a  prehensile  oro-an,  the  thoracic  portion  of 
the  column  is  situate  near  its  posterior  extremity.  Whilst  in  quad- 
rupeds aud  reptiles  balanced  on  two  pairs  of  extremities,  the  solid 
portion  of  their  trunk  is  placed  near  the  middle  of  their  column. 

PISCES. 

The  bones  of  fishes  closely  resemble  those  of  the  higher  grades 
of  organisation  in  their  embryotic  state,  not  only  in  their  soft  carti- 
laginous character,  but  also  in  the  isolated  condition  of  their  several 
centres  of  ossification,  especially  in  the  complicated  bones  of  the 
head.  The  bones  of  the  cartilaginous  tribes  are  composed  of  water, 
gelatine,  and  the  sulphate,  subcarbonate  and  chloruret  of  soda; 
whilst  the  more  dense  bones  of  the  osseous  fishes  are  indurated  and 
strengthened  by  the  more  insoluble  phosphates.  As  the  human 
embryo  originally  consists  almost  exclusively  of  the  vertebral 
column,  so  also  in  fishes  we  find  that  the  spine,  and  the  head,  which 
is  only  an  increased  development  of  it,  constitute  the  most  impor- 
tant parts  of  the  skeleton. 

Spine. — The  vertebrae  in  this  class  are  very  numerous,  and  may 
be  divided  into  the  abdominal  and  caudal.  The  bodies  of  the  verte- 
bras are  the  elements  first  developed ;  they  are  the  most  important,  and 
form  almost  the  entire  of  the  skeleton  in  the  lowest  species  of  cartila- 
ginous fishes.  They  are  concave  on  both  surfaces  ;  consequently 
enclose  large  spaces,  filled  with  a  thin  gelatinous  fluid  ;  and  in  many 
of  the  cartilaginous  species,  the  inter- vertebral  substances  communi- 
cate and  form  a  continuous  elastic  chord  passing  through  the  entire 
column  as  in  the  lamprey.  The  spinous  processes  of  the  abdominal 
vertebras  are  very  long  superiorly,  and  assist,  by  their  shanks,  to 
form  the  spinal  canal ;  whilst  the  caudal  vertebrae  are  distinguished 
by  having  long  spinal  processes  both  above  and  below.  Between 
the  roots  of  the  inferior  spinous  processes  there  is  enclosed  a  simi- 
lar canal,  but  larger  for  the  passage  of  the  great  systemic  artery. 

The  vertebral  column  in  fishes  is  constructed  in  such  a  manner 
as  to  give  considerable  perpendicular  extent  to  the  trunk,  and  thus 
favour  their  horizontal  mode  of  progression.  The  number  of  ver- 
tebra varies  greatly;  thus  in  the  carp  we  find  41,  in  the  burbot  57, 
in  the  eel  115.  and  in  the  shark  as  many  as  207.  In  the  osseous 
fishes,  the  ribs  form  an  upper  and  a  lower  range ;  the  latter  are 
better  developed  and  more  uniform  in  their  existence  than  the  former. 
The  number  of  ribs  is  generally  determined  by  that  of  the  abdo- 
minal vertebrae.  In  some,  however,  as  the  chaetodon,  scomber,  &c, 
the  caudal  vertebrae  are  furnished  with  ribs.  These  bones  articulate 
with  one  vertebra  only,  as  a  consequence  of  which  they  enjoy  but 
little  motion,  and  are  but  slightly  subservient  to  respiration.  In  the 
shark  they  are  cartilaginous  ;  in  the  carp  they  are  long  and  firm  ; 
in  the  eel  short  and  slender  ;  and  in  many  genera,  as  the  raia,  fis- 
tularia,  &c.,  they  are  almost  wholly  absent.     The  sternum,  when 


16  EVERS'S  COMPARATIVE  ANATOMY. 

present,  consists,  as  described  by  Meckel,  of  a  variable  number  of 
V-shaped  pieces,  pointed  downwards  and  overlapping  each  other. 
This  rudimentary  bone  is  best  seen  in  the  herring  and  the  dory. 

Head. — To  the  researches  of  Oken,  Meckel,  Cams,  Blainville, 
&c,  we  are  indebted  for  the  important  fact  that  the  cranium,  is 
nothing  more  than  a  highly  developed  portion  of  the  vertebral 
column.  The  composition  of  the  cranium  in  the  cartilaginous 
fishes  is  very  simple;  in  many,  as  in  the  skate,  consisting  chiefly  of 
one  large  piece.  In  the  osseous  tribes,  on  the  contrary,  the  com- 
ponent parts  are  very  numerous — amounting  to  80  in  the  head  of 
the  perch.  The  bodies  of  the  vertebras  continue  forward  in  a  straight 
line  with  the  spine  along  the  base  of  the  scull,  forming  the  basilar 
part  of  the  occipital,  the  body  of  the  sphenoid,  and  the  ethmoid 
bones.  In  the  bony  fishes  the  cranium  is  remarkable  for  being  thin, 
diaphanous,  elastic  and  having  its  elements  united  by  squamous 
sutures,  which  favours  the  extension  of  the  period  of  growth  of  each 
part.  The  cavity  of  the  cranium  is  occupied  chiefly  by  the  cellular 
tissue  of  the  arachnoid  coat;  the  brain  occupying  but  a  small  por- 
tion of  the  base  of  the  skull. 

The  bones  of  the  face  present  but  few  peculiarities.  The  inter- 
maxillary bone  consists  of  three  triangular  pieces  inserted  between 
the  vomer,  the  palate,  the  nasal,  and  the  superior  maxillary  bones. 
The  central  piece  is  generally  cartilaginous.  In  connection  with 
the  upper  jaw,  we  have  to  notice  the  os  quadratum  ;  this  is  composed 
of  several  pieces,  which  closely  resemble  the  ascending  process  of 
the  lower  jaw  in  man.  The  three  portions  of  which  it  is  mainly 
composed  are  articulated,  one  to  the  inferior  maxilla  and  palate 
bone,  the  second  to  the  temporal  bone,  while  the  third  consists  of  a 
thin  round  plate,  and  is  called  os  discoideum.  Behind  the  lower 
jaw,  and  connected  to  the  os  quadratum,  is  the  operculum.  This 
is  a  plate  of  bone  usually  composed  of  four  pieces,  which  have  been 
considered  analogous  to  the  bones  of  the  tympanum,  on  account  of 
the  absence  of  this  cavity  from  the  ears  of  fishes  ;  others  have 
regarded  it  as  a  portion  of  the  lower  jaw.  Be  this  as  it  may  we  find 
the  operculum  covering  the  respiratory  apparatus  in  the  same  man- 
ner as  the  shells  of  bivalves  cover  the  subjacent  gills. 

The  os  hyoides  reaches  a  high  degree  of  development  here,  as  in 
all  water  breathing  vertebrata  ;  it  consists  of  a  body  or  lingual  bone, 
and  five  pieces  on  either  side  of  it:  it  is  suspended  from  the  tem- 
poral bones  ;  and  it  is,  by  its  free  antero-posterior  motions  that  res- 
piration is  effected  in  fishes,  and  in  amphibia,  as  will  be  shown 
hereafter.  It  forms  an  arch,  having  the  lower  jaw  above  it,  and  the 
scapular  and  coracoid  bones  below.  Its  sides  support  the  four  pairs 
of  branchial  arches,  and  externally  it  has  attached  to  it  the  opercular 
membrane. 

Extremities. — In  fishes  fins  supply  the  place  of  extremities  ;  the 
anterior  corresponding  to  the  arms,  and  the  posterior  to  the  legs. 
They  are  named  according  to  the  parts  they  are  attached  to,  as 
dorsal,  pectoral,  ventral,  caudal,  and  anal  fins.     The  anterior  or 


VERTEBRATA.  17 

pectoral  fins  are  larger  and  more  uniform  in  their  existence  than 
the  posterior;  they  also  commence  their  development  at  an  earlier 
period;  in  all  of  which  they  resemble  the  embryo  of  the  higher 
classes.  The  ventral  fins  are  wanting  in  the  apodes,  as  well  a*s  in 
several  species  of  other  orders  ;  whilst  the  pectoral  fins  are  generally 
present. 

The  anterior  fins  are  generally  joined  to  the  back  of  the  skull  by- 
means  of  an  osseous  belt,  formed  behind  by  the  scapula,  and  in  front 
by  the  coracoid  bones.  A  humerus,  generally  long  and  angular,  is 
attached  to  these  above,  and  to  the  radius  and'ulna  below.  To  these 
succeed  the  carpal  bones,  and  the  member  is  terminated  by  long 
and  numerous  phalanges.  The  posterior  members,  or  ventral  fins, 
have  no  connection  to  the  spine,  but  are  suspended  from  the  rib-like 
iliac  bones,  and  placed  on  the  lower  part  of  the  trunk,  at  a  variable 
distance  between  the  head  and  anus.  The  presence  of  a  sacrum 
in  this  class  would  be  injurious  to  the  free  motion  required  in 
swimming.  In  the  abdominal  fishes  the  pelvic  bones  are  uncon- 
nected to  the  skeleton  :  and  in  the  apodal  families  they  are  wholly 
absent.  The  long  phalanges  of  the  feet  are  attached  directly  to  the 
pelvic  bones,  there  being  rarely  a  trace  of  intermediate  bones 
developed. 

The  want  of  symmetry  observed  in  the  skeletons  of  many  fishes 
forms  a  singular  peculiarity  in  this  class.  In  the  pleuronectes,  for 
instance,  one  side  is  turned  upwards,  instead  of  the  back  ;  both 
eyes  are  placed  on  the  same  side;  the  cranial  vertebra-  seem 
twisted  in  their  long  axis  ;  and  the  lower  part  of  the  head  is  imper- 
fectly developed.  The  bones,  especially  the  intermaxillary,  are 
much  larger  on  the  side  opposite  to  that  on  which  the  eyes  are 
placed. 

RECAPITULATION. 

1.  The  bones  of  fishes  resemble  the  embryotic  condition  of  the 
osseous  system  in  the  higher  classes  of  animals. 

2.  The  spine  is  the  most  important  part  of  their  skeleton. 

3.  The  spinal  column  enjoys  very  (ree  motion,  chiefly  in  the 
lateral  direction. 

4.  The  construction  of  the  head  is  as  simple  in  the  cartilaginous 
as  it  is  complex  in  the  osseous  fishes. 

5.  The  os  hyoicles  is  greatly  developed  to  support  the  branchial 
apparatus. 

6.  The  anterior  fins  are  larger,  earlier  developed,  and  more  uni- 
form in  their  existence  than  the  posterior. 

7.  The  pelvic  bones  and  posterior  fins  are  absent  from  the  ske- 
letons of  many  cartilaginous  fishes. 

8.  Want  of  symmetry  is  a  striking  peculiarity  in  the  skeletons 
of  many  fishes. 

'      *  evers  2 


18  EVERS'S  COMPARATIVE  ANATOMY. 


AMPHIBIA. 

In  the  Batrachia  the  ribs  are  almost  wholly  absent ;  it  is  only 
in  the  rana  pipa  and  the  salamanders  that  small  cartilaginous 
appendages  are  found  attached  to  the  transverse  processes  of  some 
of  the  vertebrae.  In  these  animals  the  spine  consists  of  dorsal, 
sacral,  and  caudal  portions — the  distinction  being  marked  by  the 
connection  of  one  of  the  vertebras  to  the  ilium  on  each  side.  The 
salamander  has  fourteen  dorsal,  one  sacral,  and  twenty-seven  cau- 
dal vertebrae ;  in  the  common  frog  there  are  only  nine  vertebrae ; 
and  in  the  rana  pipa  but  eight;  whilst  the  siren  has  forty-three  in 
the  trunk,  and  about  forty-five  in  the  tail ;  from  the  second  to  the 
eighth  inclusive  have  rudimentary  ribs  attached  to  them.  The 
bodies  of  the  vertebrae  are  concave  on  their  surfaces;  so  that,  when 
in  apposition,  they  give  rise  to  the  existence  of  an  intervertebral 
oval  cavity  filled  by  a  gelatinous  mass. 

When  we  consider  the  habits,  food,  and  mode  of  progression,  of 
the  frog — that  its  movements,  which  are  chiefly  on  land,  are  both 
active  and  extensive,  as  well  for  the  purpose  of  seizing  its  prey  as 
of  escaping  from  danger — it  becomes  obvious  why  its  spine  should 
be  short  and  firmly  anchylosed — how  the  presence  of  a  tail  would 
be  worse  than  useless,  and  why  a  necessity  exists  for  a  full  deve- 
lopment of  the  posterior  extremities.  The  absence  of  ribs  will 
hereafter  be  accounted  for  by  an  interesting  peculiarity  in  the  func- 
tion of  respiration. 

Cranium. — The  elements  composing  this  cavity  are  remarkable 
for  remaining  permanently  ununited,  a  state  of  things  which  is 
strikingly  imitated  during  the  progress  of  the  development  of  these 
parts  in  the  higher  orders  of  animals.  The  maxillary,  intermaxil- 
lary, tympanic,  and  jugal  bones  are  greatly  expanded,  in  the 
transverse  direction,  giving  the  face  a  flattened  appearance.  The 
lower  jaw  consists  of  three  pieces  on  each  side. 

Of  all  parts  of  the  osseous  system  of  this  class,  there  is  none  so 
interesting  as  the  os  hyoides,  on  account  of  the  changes  to  which 
it  is  subjected  during  the  transit  of  the  amphibia  from  the  pisciform 
to  the  reptile  state.  The  branchiae  are  external,  supported  by  car- 
tilaginous arches  connected  with  os  hyoides.  As  the  age  of 
the  tadpole  increases,  the  branchiae  disappear,  the  lungs  become 
developed,  and  the  os  hyoides  grows,  from  a  small  rhomboidal 
point,  to  the  large  size  and  peculiar  from  which  it  presents  in  the 
full-grown  frog. 

Anterior  extremity. — The  shoulder  of  a  frog  consists  of  scapula, 
clavicle,  and  coracoid  bone,  all  of  which  unite  to  form  the  glenoid 
cavity.  The  humerus  is  short  and  thick,  having  a  round  head 
above,  received  by  the  glenoid  cavity,  and  also  a  spherical  extremity 
below,  to  articulate  with  the  bones  of  the  fore-arm,  which  consists 
of  radius  and  ulna  so  united  that  a  faint  line  indicates  their  former 
separation.     The  carpal  bones  are  six ;  the  metacarpal,  four.    The 


VERTEBRATA.  19 

middle  and  index  fingers  have  each  two  phalanges,  the  others 
three. 

The  posterior  extremity,  for  reasons  before  assigned,  reaches  a 
high  degree  of  development.  The  cotyloid  cavity  is  constituted  by  the 
ilium,  ischium,  and  pubis.  The  femur  is  long  and  cylindrical.  The 
tibia  and  fibula  are  consolidated  into  one  bone,  and  joined  inferiorly 
to  two  bones  representing  astragalus  and  os  calcis.  Between  these 
and  the  long  metatarsal  bones  are  placed  four  small,  irregular 
bones.  Of  the  rive  toes,  the  internal  is  best  developed,  and  sus- 
tains three  long,  slender  phalanges. 

The  structure  and  form  of  the  salamander,  proteus,  and  siren, 
are  well  contrasted  with  those  of  the  froo\  In  the  former  animals, 
the  spinal  column  attains  a  high  state  of  development :  the  extre- 
mities are  reduced  to  a  rudi mental  type.  The  bones  of  the  fore- 
arm and  leg,  instead  of  being  anchylosed  as  in  the  frog,  maintain 
a  permanent  state  of  separation.  The  toes,  which  are  four  in 
number,  are  but  slightly  developed.  The  whole  economy  of  the 
frog  is  admirably  organised  for  rapid  terrestrial  progression,  while 
that  of  the  other  animals  is  designed  to  favour  their  movements 
through  a  watery  element. 

Who  can  fail  to  observe  the  extreme  wisdom  manifested  in  the 
metamorphosis  of  these  animals?  In  the  early  part  of  their  exist- 
ence, and  while  they  enjoy  an  aquatic  mode  of  life,  their  organi- 
sation is  in  due  accordance ;  at  first  their  members  are  scarcely 
perceptible,  whilst  their  tail  is  of  great  length,  and  continues  so  in 
those  destined  to  continue  their  watery  habitation  ;  but  in  the  frog, 
(fee,  which  are  to  breathe  by  lungs,  the  tail  is  gradually  removed 
by  absorption,  and  the  extremities,  particularly  the  posterior,  un- 
dergo a  rapid  evolution. 


REPTILIA. 

Chelonia.—These  reptiles  present  a  tolerably  perfect  form  of  ske- 
leton. Their  spine  consists  of  eight  cervical,  fourteen  dorsal,  three 
sacral,  and  from  twenty  to  thirty  caudal  vertebrae.  There  are 
eight  pairs  of  immovable  ribs,  united  to  each  other  by  sutures,  and 
attached  between  the  bodies  of  the  vertebrae.  By  the  union  of  the 
ribs  with  each  other,  and  with  the  spinous  processes  of  the  dorsal 
vertebras,  they  form  the  upper  shield  or  carapace.  The  nine  pieces 
of  the  sternum  which  are  movable  in  the  turtle,  form  the  lower 
shield  or  plastron.  This  unyielding  frame-work  is  well  suited  to 
resist  pressure,  as  well  as  to  favour  their  muscular  movements  on 
land,  whilst  the  mobility  of  the  several  elements  of  the  sternum  in 
the  aquatic  species  is  applicable  to  their  extensive  respiration  in  that 
dense  element. 

The  bones  of  the  head  are  firmly  united  by  sutures.  The  occi- 
pital condyle  presents  three  facets,  formed  by  the  basilar  and  the 
two  condyloid  portions.  The  inter-maxillary  bones  are  narrow, 
but  present  a  large  palatine  surface.     The  bones  of  the  ear  are 


20  EVERS'S  COMPARATIVE  ANATOMY. 

anchylosed,  and  the  body  and  cornua  of  the  os  hyoides  are  fully 
developed. 

In  the  anterior  extremity,  which  is  attached  to  the  inner  side  of 
the  chest,  we  distinguish  scapula  and  clavicle  united  by  suture  ; 
humerus  twisted,  with  a  large  articular  condyle;  radius  and  ulna 
short,  strong,  and  expanded  inferiorly,  fixed  in  a  state  of  pronation; 
carpal  bones,  sometimes  as  many  as  ten,  arranged  in  three  rows; 
five  short  metacarpal  bones;  and  the  phalanges,  two  for  the  thumb 
and  last  finger,  and  three  for  each  of  the  others. 

The  ilia  are  long  and  cylindrical  in  the  land  tortoise ;  the  pubis 
and  ischium  broad  and  flat.  The  femur  presents  indications  of 
trochanters,  as  in  man  ;  its  head  is  large,  and  joins  the  shaft  at  a 
right  angle.  There  is  no  round  ligament  in  the  hip,  though  rudi- 
ments of  semilunar  cartilages  connected  to  crucial  ligaments  in  the 
knee.  The  tibia  and  fibula  are  separate.  The  metacarpal  bones 
are  five,  and  the  number  and  arrangement  of  the  phalanges  the 
same  as  observed  in  the  phalanges  of  the  fingers,  with  the  exception 
of  the  outer  toe,  which  is  generally  rudimentary.  In  the  aquatic 
chelonia,  the  bones  of  the  extremities  are  longer,  straighter,  and 
more  slender  than  in  the  land  species. 

Ophidia. — The  skeleton  in  serpents  consists  of  little  more  than  a 
vertebral  column,  possessing  such  a  degree  of  mobility  as  enables 
them  to  creep  with  speed  along  the  surface,  to  swim  through  the 
waters,  to  spring  into  the  air,  to  climb  trees,  and  to  combat  with  and 
conquer  their  prey.  Extremities  are  here  wholly  absent,  and  the 
spinal  column  and  ribs  constitute  the  sole  organs  of  progressive 
motion.  For  this  reason  the  spine  is  characterised  by  immense 
strength  and  great  mobility.  The  vertebrae  are  more  numerous 
in  this  than  in  any  other  class  of  animals,  being  49  in  the  anguis 
fragilis,  or  blind  worm  ;  201  in  the  crotalus  horrid  us,  or  rattle-snake  ; 
and  316  in  the  coluber  natrix.  The  bodies  of  the  vertebrae  have 
ball  and  socket  articulations,  so  disposed  as  to  admit  of  free  lateral, 
but  limited  antero-posterior  motion.  The  ribs  of  serpents  are  tubu- 
lar, narrow  and  compressed  from  before  backwards.  Their  head 
presents  a  broad,  arched,  concave  surface,  to  articulate  with  the 
rounded,  prominent,  transverse  processes  of  the  vertebra?,  whilst 
their  ventral  extremity  tapers  to  end  in  a  thin,  flexible  cartilage. 
The  ribs  extend  from  the  atlas  to  the  anus,  and  are  32  pairs  in  the 
blind  worm,  175  in  the  rattle-snake,  and  204  in  the  coluber  natrix. 
They  are  all  of  the  false  kind,  there  being  no  rudiment  of  sternum, 
except  in  the  ophisaurus  and  blind  worm  alone,  in  which  also  faint 
traces  of  shoulder  and  pelvis  may  be  discerned. 

The  head  resembles  the  preceding  order  (or  that  of  the  chelonia) 
in  the  small  size  of  the  cranium,  whilst  the  multiplicity  and  detached 
condition  of  its  bones  ally  it  to  the  fishy  tribes.  This  loose  state  of 
the  component  elements  of  the  head  is  necessary  in  serpents,  for, 
being  deprived  of  organs  of  prehension,  they  are  compelled  to  swallow 
their  prey  entire.  As  a  consequence  of  the  looseness  of  the  other 
bones,  the  two  parietals  are  anchylosed  along  the  median  line,  to 


VERTEBRATA.  21 

protect  the  brain  during  the  exposure  of  these  animals  to  the 
trampling  of  quadrupeds,  &c,  whilst  concealed  in  their  natural 
haunts.  Their  teeth  are  small,  conical,  and  sharp  ;  they  are  placed 
in  the  two  maxillary,  the  intermaxillary,  and  the  palate  bones. 

Sauria. — In  this  order  we  meet  with  a  more  perfect  development 
of  skeleton  than  in  the  last,  as  they  possess  a  sternum,  a  scapular 
and  pelvic  apparatus,  together  with  atlantal  and  sacral  extremities. 
The  lacerta  iguana  presents  5  cervical,  11  dorsal,  9  lumbar,  2 
sacral,  and  72  caudal  vertebrae  ;  the  crocodile  of  the  Nile  7  cervical, 
12  dorsal,  5  lumbar,  2  sacral,  and  34  caudal — articulated  by  ball 
and  socket.  There  are  false  ribs  behind  and  before  the  true  ones. 
In  the  chameleon  there  are  17  pairs ;  in  the  crocodile  12.  The 
sternum  is  prolonged  posteriorly  as  far  as  the  pubis,  and  has  attached 
to  it  five  pairs  of  cartilaginous  arches,  for  the  purpose  of  supporting 
the  abdomen. 

The  head  is  extended  forwards  in  a  line  with  the  spine,  as  in  the 
other  inferior  vertebrata ;  like  these,  also,  its  component  elements 
are  loosely  connected.  As  in  serpents,  the  basilar  condyle  is  elon- 
gated transversely,  and  the  parietal  bones  anchylosed.  The  lower 
jaw  consists  of  six  pieces  on  each  side  ;  and  here,  as  in  serpents, 
the  prehensile  teeth  are  attached  by  broad  base  to  the  surface  of  the 
jaw,  and  the  new  teeth  rise  by  the  side  of  the  old,  and  not  in  their 
interior  as  in  the  crocodile. 

Anterior  extremity. — The  scapula  is  broad,  thin,  and  curved. 
The  acromion  is  a  distinct  bone,  and  the  clavicles  are  anchylosed 
in  form  of  a  cross,  on  the  front  of  the  sternum.  The  humerus  is 
expanded  at  its  extremities,  and  the  same  form  as  in  man ;  the  ulna 
is  without  an  olecranon,  stronger  than  the  radius,  and  separated  from 
it  below.  There  are  from  four  to  nine  bones  in  the  carpus,  five 
in  the  metacarpus;  and  the  phalanges  are,  two  for  the  thumb, 
three  for  the  second  and  last  fingers,  and  four  for  each  of  the 
others. 

Posterior  extremity. — The  three  portions  of  the  os  innominatum 
contribute  to  the  formation  of  the  cotyloid  cavity.  The  ossa  pubis 
and  ischii  form  a  lengthened  symphisis  in  front;  and  the  spine  of 
the  iliac  bones  is  extended  backwards  along  each  side  of  the  sacrum. 
From  the  front  of  the  pubic  bone  a  process  passes  up  towards  the 
sternum  as  in  the  marsupiales.  The  head  of  the  femur  is  com- 
pressed and  directed  forwards  ;  the  great  trochanter  is  also  flat  and 
turned  towards  the  tibia.  The  patella  is  small  ;  the  tibia  short, 
thick,  and  curved ;  the  fibula  slender  in  the  centre,  expanded  at  its 
extremities,  and  apart  from  the  tibia.  In  the  crocodile  there  are  five 
bones  in  the  tarsus,  four  in  the  metatarsus,  and  the  toes  are  so 
arranged  that  the  most  internal  sustains  two  phalanges,  the  second 
three,  and  the  third  and  fourth,  four  each. 

In  the  skeletons  of  the  nilotic  crocodiles,  alligators,  and  other 
reptiles  destined  to  swim  by  the  lateral  movements  of  a  muscular 
tail  and  long  webbed  feet,  their  long  bones  are  filled  with  a  thin 
oily  marrow,  and  the  bones  of  the  head  firmly  united. 


22 


RECAPITULATION. — Amphibia. 


1.  In  amphibia  rudiments  of  ribs  only  are  met  with. 

2.  Vertebrae  range  from  eight  in  the  rana  pipa  to  eighty-nine  in 
the  siren. 

3.  In  the  frog,  the  extremities,  especially  the  posterior,  are  fully 
developed  ;  the  tail  is  absorbed. 

4.  Salamander,  proteus,  and  siren,  may  be  well  contrasted  with 
the  frog  ;  in  the  former  the  spinal  column  attains  and  maintains  a 
high  degree  of  development,  whilst  their  members  are  reduced  to  a 
mere  rndimental  type. 

5.  The  bones  of  the  cranium  remain  loosely  united  through  life. 

6.  The  os  hyoides  undergoes  remarkable  changes  during  the 
metamorphosis  of  the  animal  from  the  pisciform  to  the  reptile 
state. 

recapitulation. — Reptilia. 

1.  The  vertebrae  and  ribs  are  more  numerous"  than  in  any  other 
class  of  animals. 

2.  The  chelonia  differ  from  the  sauria  in  having  immovable  ribs, 
and  from  the  ophidia  in  having  arms  and  legs. 

3.  The  bones  of  the  head  generally  maintain  a  permanent  state 
of  separation,  except  the  parietals  which  are  firmly  auchylosed. 

AVES. 

As  in  this  department  of  my  subject  I  avail  myself  of  much  of  the 
valuable  matter  contained  in  the  article,  Aves,  in  the  Cyclopaedia  of 
Anatomy  and  Physiology,  by  that  clear,  accurate,  and  scientific 
writer,  Mr.  Owen,  it  becomes  necessary  to  state  that  he  divides  the 
class  into  the  following  orders  : — 

1.  Raptores,  birds  of  prey,  or  raveners  ;  2.  Insessores,  perchers  ; 
3.  Scansores,  climbers ;  4.  Rasores,  scratchers ;  5.  Cursores, 
coursers;  6.  Grallatores,  waders  ;  and  7.  Natatores,  swimmers. 

Positive  characters  of  the  class. — Animal,  vertebrated,  oviparous, 
biped:  anterior  extremities  organised  for  flight;  integument  plu- 
mose ;  blood  red  and  warm ;  respiration  and  circulation  double  ; 
lungs  fixed  and  perforated. 

Negative  characters. — No  auricles,  teeth,  lips,  epiglottis,  dia- 
phragm, fornix,  corpus  callosum,  or  scrotum. 

The  bones  of  birds  are  remarkable  for  being  permeated  by  atmo- 
spheric air,  for  their  compact  and  laminated  texture,  their  white 
colour,  and  their  fragility,  owing  to  a  preponderance  of  phosphate  of 
lime. 

The  vertebrae  are  the  first  bones  observed  in  the  development  of 
the  osseous  system  of  birds,  and  of  all  parts  of  this  system,  they 
present  the  fewest  variations.  The  spine  here  consists  of  cervical, 
dorsal,  sacral  and  caudal  portions.     The  first  and  last  are  the  most 


VERTEBRATA.  23 

movable,  and  in  many  species  of  the  dorsal  and  caudal  portions 
admit  of  no  motion  at  all.  This  fixity  facilitates  the  flight  of  the 
bird,  whilst  the  length  and  mobility  of  the  cervical  portion  of  the 
spine  compensate,  in  some  degree,  for  the  unfitness  of  the  anterior 
members  to  the  purposes  of  prehension,  &c. 

The  cervical  portion  of  the  spine  is  generally  composed  of  a  greater 
number  of  vertebrae  than  any  of  the  other  divisions  ;  they  are  not 
fewer  than  nine,  as  observed  in  the  sparrow,  nor  more  than  twenty- 
three,  as  in  the  swan. 

The  bodies  lock  into  each  other,  and  are  so  disposed  as  to  allow 
the  superior  and  inferior  ones  to  move  forwards,  and  the  middle 
backwards.  The  transverse  processes  are  long,  and  have  rudi- 
mentary ribs  connected  to  them  ;  these  are  particularly  well  deve- 
loped in  rapacious  birds,  and  hence  the  great  breadth  of  their  necks. 
The  atlas  is  a  simple  ring,  generally  articulated  to  the  occipital 
tubercle  by  a  single  facet;  but  the  penguin  and  ostrich  have  two 
other  facets  continuous  with  the  central  one.  From  the  dentata 
down,  a  movable  inter-articular  cartilage  is  found,  as  in  the  joint  of 
the  lower  jaw  of  the  mammalia. 

The  dorsal  vertebrae  range  from  six  in  the  bull-finch  to  eleven  as 
seen  in  the  swan.  The  bodies  of  these  vertebrae  are  short  and 
compressed  laterally,  except  in  the  ostrich.  The  transverse  pro- 
cesses are  greatly  developed.  The  anterior  cartilaginous  surface  is 
convex  in  the  vertical  direction,  concave  in  the  transverse,  and 
connected  by  fibrous  capsules  and  synovial  membranes.  Most 
birds  have  the  middle  and  lower  vertebrae  anchylosed  ;  even  the 
transverse  and  spinous  processes  of  the  superior  are  anchylosed  in 
those  birds  requiring  great  fixation  of  the  trunk  ;  while  in  those  that 
cannot  fly,  as  the  penguins,  they  are  all  movable. 

The  sacral  vertebrae  are  firmly  anchylosed  with  one  another, 
and  with  the  ilia  laterally;  consequently  it  is  difficult  to  determine 
their  real  number  ;  it  is  not,  however,  greater  than  nineteen,  as 
seen  in  the  emeu  and  cassowary,  nor  less  ihan  eight,  as  observed  in 
the  hoopoe.  The  bodies  of  these  vertebrae  are  broad,  but  shallow, 
and  the  canal  greatly  enlarged,  to  correspond  to  the  size  of  the 
chord,  which  here  supplies  nerves  to  the  posterior  extremities. 
When  it  is  considered  that  the  head,  posterior  members,  viscera,  &c, 
are  suspended  in  flight  from  this  central  portion  of  the  trunk,  the 
necessity  for  the  mechanism  consolidating  these  vertebrae  will  be 
readily  appreciated. 

The  coccygeal  vertebrae  are  generally  movable,  and  from  five 
to  nine  in  number.  With  the  exception  of  the  last,  they  are  broad, 
short,  and  perforated  for  the  spinal  marrow.  The  last  has  no  pro- 
cesses ;  it  is  compressed  laterally,  and  terminates  above  and  below 
in  a  sharp  edge  ;  it  supports  the  coccygeal  oil-gland,  and  affords  a 
firm  basis  to  the  tail  feathers,  or  retrices  of  Linnaeus.  These  bones 
possess  ligamentous  connections,  except  the  sixth  and  seventh  which 
re  provided  with  a  capsule  and  synovial  fluid. 


24 


EVERS'S  COMPARATIVE  ANATOMY. 


TABLE  OF  THE  VERTEBRAE  IN  BIRDS. 


ORDER    RAPTORES 

VBRTEBR.K. 

ORDER    RASORES. 

VERTEBRAE 

Species. 

Derv. 

Dor. 

Sac. 

Cau. 

Species . 

Cerv. 

Dor. 

Sac. 

Cau. 

Vulture, 

13 

7 

11 

7 

Crested  Curas- 

Eagle, 

13 

8 

11 

8 

sow, 

15 

8 

10 

7 

Sparrow-hawk, 

11 

8 

11 

8 

ORDER    CCRSORES 

Kite, 

12 

8 

11 

8 

Ostrich, 

'  18 

10 

17 

9 

Hawk-owl, 

11 

8 

11 

8 

Cassowary, 

16 

10 

19 

7 

ORDER    INSESSORES. 

Emeu, 

19 

9 

19 

9 

Fly-catcher, 

10 

8 

10 

8 

ORDER    GRALLATORES. 

Blackbird, 

11 

8 

10 

7 

Heron, 

18 

7 

10 

7 

Crow, 

13 

8 

13 

7 

Crane, 

19 

9 

12 

7 

Magpie, 

13 

8 

13 

8 

Spoonbill, 

17 

7 

14 

8 

Jay, 

12 

7 

11 

8 

Avoset, 

14 

9 

10 

8 

Starling, 

10 

8 

10 

9 

Plover, 

15 

8 

10 

7 

Bull-finch, 

10 

6 

11 

6 

Woodcock, 

18 

7 

13 

8 

Sparrow, 
Goldfinch, 

9 

9 

10 

7 

Curlew, 

13 

8 

10 

8 

11 

8 

11 

8 

Oyster-catcher, 

12 

9 

15 

7 

Lark, 

11 

9 

10 

7 

Coot, 

15 

10 

13 

8 

Redbreast, 

10 

8 

10 

8 

Flamingo, 

18 

7 

12 

7 

Swallow, 

11 

8 

11 

9 

ORDER    NATATORIS. 

Humming-bird, 

14 

9 

10 

8 

Pelican, 

16 

7 

14 

7 

Kingfisher, 

12 

7 

11 

7 

Cormorant, 

16 

9 

14 

8 

ORDER    "CANSORES. 

Gull, 

12 

8 

11 

8 

Woodpecker, 

12 

8 

10 

9 

Catarrhactes, 

13 

9 

13 

8 

Parrot, 

11 

9 

11 

8 

Swan, 

23 

11 

14 

8 

ORDER    RASORES. 

Goose, 

15 

10 

14 

7 

Pigeon, 

13 

7 

13 

7 

Duck, 

14 

8 

15 

8 

Peacock, 

14 

7 

12 

8 

Sheldrake, 

16 

11 

11 

9 

Pheasant, 

13 

7 

15 

5 

Mergancer, 

15 

8 

13 

7 

Turkey, 

15 

7 

10 

5 

Grebe, 

14 

10 

13 

7 

Skull. — It  has  been  already  shown  that  the  bones  composing  the 
skull  of  the  crocodile,  and  other  cold  blooded  vertebrata,  were  not 
consolidated  till  a  late  period  of  life,  giving  rise  to  some  difficulty 
in  tracing  a  correspondence  between  their  bones  and  those  of  a 
higher  order.  A  still  greater  difficulty  is  experienced  in  determining 
the  component  parts  of  the  head  in  birds  ;  for  in  them  the  bones  of 
the  skull  are  anchylosed,  and  every  trace  of  suture  effaced  at  an 
early  epoch  ;  therefore,  in  order  to  accomplish  their  perfect  separa- 
tion, it  must  be  undertaken  at  an  early  period  of  their  existence. 

In  the  majority  of  birds,  the  head  is  articulated  to  the  spine,  by 
means  of  a  single  hemispherical  tubercle  on  the  basilar  process  of 
the  occipital  bone  ;  but  in  the  penguin  and  ostrich,  the  condyloid 
portions  contribute  to  its  formation,  and  the  articulation  is  such  as 
to  admit  of  very  great  freedom  of  motion. 

The  occipital  bone  is  originally  composed  of  four  pieces,  basilar, 
spinous  and  two  condyloid.  The  temporal  consists  of  the  petrous, 
squamous,  and  tympanic  portions  ;  the  last  is  movably  articulated 
to  the  inferior  part  of  the  squamous  portion,  and  is  sometimes  called 
osquadratum.  The  alae  majores  of  the  sphenoid  bone  remain  a 
long  time  separate,  and  are  called  interarticular,  or  omoid  bones. 
The  remaining  bones  of  the  skull  present  no  remarkable  peculiarities 


VERTEBRATA. 


25 


save  that  they  are  all  early  and  firmly  anchylosed,  with  the  excep- 
tion of  the  tympanic  bone. 

The  bones  of  the  face  correspond  in  number  and  position  to  those 
of  the  mammalia,  especially  the  order  rodentia.  They  are  movably 
connected  with  the  bones  of  the  cranium,  and  remain  separate  to  a 
much  later  period.  The  upper  mandible  is  chiefly  characterised  by 
the  presence  of  the  intermaxillary  bone.  This  consists  of  three 
processes,  a  central,  and  two  lateral ;  the  former  passes  up  between 
the  superior  maxillary  bones,  and  becomes  joined  to  the  nasal  and 
ethmoid  ;  this  union  is  ligamentous  in  the  parrot,  and  those  birds 
that  apply  the  upper  mandible  to  the  purposes  of  climbing.  The 
two  lateral  processes  of  the  inter-maxillary  bone,  extend  upwards 
and  backwards  external  to  the  superior  maxillary  bones,  to  which 
they  are  firmly  united. 

There  are  few  more  ingenious  or  beautiful  pieces  of  mechanism 
than  that  by  which  the  mouth  of  a  bird  is  opened.  The  tympanic 
bone  as  before  observed,  never  anchyloses  with  the  other  elements 
of  the  temporal;  on  the  contrary,  it  articulates  with  the  zygomatic 
portion  of  the  latter  bone,  by  two  transverse  condyles  above  ;  below 
it  articulates  by  a  broad  surface  with  the  upper  and  back  part  of  the 
lower  jaw,  while  in  front  and  near  its  lower  extremity,  it  has 
applied  to  it  the  long,  slender  malar  bone  which  reaches  to  the 
superior  maxilla.  When  the  tympanic  bone  is  drawn  forwards, 
either  by  the  action  of  the  pterygoid  muscles  attached  to  it,  or  by 
the  depression  of  the  lower  jaw,  the  malar  bone  is  advanced  against 
the  superior  mandible,  which  is  elevated  at  the  same  moment  that 
the  lower  one  is  depressed.  The  moment  the  pressure  ceases  to 
exist  below,  the  elasticity  of  the  union  of  the  intermaxillary  bone 
with  the  cranium  restores  the  upper  mandible  to  its  situation. 

The  inferior  maxilla  originally  consists  of  six  pieces  on  each 
side,  named  anterior  dental,  two  condyloid,  angular,  supra-angular, 
and  opercular.  As  this  bone,  together  with  the  upper  jaw,  forms 
the  chief  organ  of  prehension  in  birds,  it  is  but  natural  to  expect 
that  it  shall  present  numerous  modifications,  indicative  of  the  food 
and  habits  of  each  species. 

There  is  more  uniformity  observed  in  the  skulls  of  birds  than  in 
any  other  class  of  the  vertebras  department.  It  generally  presents 
the  form  of  a  five  sided  pyramid,  the  base  represented  by  the  occiput, 
and  the  apex  by  the  bill.  In  the  Raptores  it  is  short,  broad,  and 
deep ;  nearly  spherical  in  the  Warblers ;  flattened,  and  of  great 
breadth,  in  the  Scansores  ;  narrow,  and  slightly  raised  in  theRaso- 
rial  birds  ;  and  remarkable  for  its  great  length  in  the  Waders. 

Thorax. — The  extent  and  energy  of  the  respiratory  function  of 
birds,  are  clearly  indicated  by  the  peculiar  and  perfect  condition  of 
this  part  of  their  osseous  system.  The  ribs,  as  in  the  mammalia, 
are  arranged  into  true  and  false,  with  this  difference,  that  the  false 
ribs  are  placed  both  above  and  below  the  true  ones.  There  is 
some,  though  not  very  great  variety  in  the  number  of  ribs  presented 
by  this  class  :  for  instance,  in  the  Insessores  we  meet  with  seven  or 


26 

eight  pairs ;  and  in  the  willock,  of  the  order  Natatores,  twelve 
pairs;  the  average  number  is  eight  or  nine  pairs.  The  true  ribs 
are  joined  to  the  sternum  by  straight  osseous  portions,  called  ster- 
nal ribs,  instead  of  by  elastic  cartilages,  and  are  movably  connected 
at  each  end.  It  is  highly  interesting  to  observe  the  mode  of  articula- 
tion of  the  vertebral  extremity  of  the  ribs.  In  such  as  require 
fixity  of  the  chest,  for  the  purposes  of  flight,  the  rib  is  articulated 
to  the  side  of  the  vertebra,  having  no  connection  to  the  inter-arti- 
cular cartilage;  but  in  the  ostrich,  and  others  of  the  cursores, 
where  the  dorsal  vertebras  preserve  their  mobility,  the  heads  of  the 
ribs  are  attached  to  the  intervertebral  spaces. 

There  is  another  interesting  fact  connected  with  the  ribs,  in 
birds  of  powerful  flight ;  it  consists  in  a  number  of  small  osseous 
plates  being  detached  from  the  posterior  margin  of  each  true  rib, 
and  passing  backwards  and  upwards  to  be  connected  to  the  suc- 
ceeding rib,  by  means  of  strong,  oblique,  fibrous  ligaments.  In 
the  ostrich,  rhea,  emeu,  and  cassowary,  these  bony  splints  present  a 
mere  rudimentary  type. 

Sternum. — The  modifications  presented  by  this  bone,  strictly 
conform  to  the  functions  which  the  anterior  extremities  are  designed 
to  execute.  Hence,  in  the  cursorial  birds  which  do  not  fly,  it  is  met 
with  in  the  form  of  a  simple  square  plate  of  bone  like  a  shield,  while  in 
those  birds  that  possess  great  powers  of  flight,  it  extends  over  the 
whole  of  the  lower  aspect  of  the  thorax  and  abdomen,  even  to  the 
pubic  bones,  and  in  order  to  afford  sufficient  space  for  the  attach- 
ment of  the  pectoral  muscles,  it  is  armed  with  a  huge  crest,  extend- 
ing the  whole  length  of  its  lower  surface.  This  crest,  or  keel,  is 
uniformly  developed  in  proportion  to  the  size  of  the  pectoral  mus- 
cles, and  hence  declares  the  power  of  the  anterior  extremities.  The 
sternum  is  sloped  obliquely  on  each  side  of  its  anterior  extremity, 
for  the  reception  of  the  clavicle,  and  in  the  centre  is  connected 
with  the  fork-bone,  either  directly  or  by  means  of  ligaments;  the 
true  ribs  are  attached  to  it  on  each  side.  The  sternum  of  the  crane 
has  within  it  a  large  cavity,  containing  several  convolutions  of  the 
trachea.  This  condition  is  repeated  in  the  wild  swan;  but  in  the 
tame  swan,  and  some  of  the  grallae,  as  the  ciconia  and  gallinae,  it 
is  but  very  feebly  developed. 

On  the  internal  surface  of  the  sternum,  chiefly  along  the  mesial 
line,  several  apertures  may  be  observed,  for  the  passage  of  air  into 
the  bone. 

Anterior  extremity. -—Here,  as  in  the  mammalia,  the  extremity 
consists  of  shoulder,  arm,  fore-arm.  and  hand.  In  the  first,  we 
recognise  a  scapula,  a  coracoid  bone,  and  a  clavicle. 

The  scapula  is  generally  a  long,  narrow  bone,  increasing  in 
thickness  as  it  approaches  the  shoulder  joint,  where  it  expands  in 
the  transverse  direction,  to  form  the  posterior  half  of  the  glenoid 
cavity ;  here  also  it  articulates  with  the  coracoid  bone  and  clavicle. 
The  direction  of  the  scapula  is  longitudinal.     In  birds  with  active 


VERTEBRATA.  27 

powers  of  flight,  it  reaches  to  the  last  rib.  while  in  the  emeu  it  covers 
only  two.     This  bone  is  broad  and  flat  in  the  penguins. 

The  coracoid.  or  posterior  clavicle,  is  a  strong  bone,  broad  in- 
feriorly.  where  it  is  received  in  a  transverse  groove  in  the  sternum  ; 
it  extends  upwards,  outwards,  and  forwards",  to  articulate  with  the 
scapula  and  clavicle.  The  glenoid  cavity  thus  resulting  from  the 
union  of  this  bone  with  the  scapula,  is  often  unequal  to^the  recep- 
tion of  the  head  of  the  humerus  ;  hence,  in  the  raptores  and  inses- 
sores,  a  small  but  distinct  bone  extends  between  the  coracoid  and 
scapula,  over  the  superior  part  of  the  cavity,|which  it  here  completes. 
It  was  discovered  by  Nitzsch,  who  called  it  the  capsular  bone. 

The  clavicles  are  subject  to  considerable  variety.  In  the  ground 
parrots  of  Australia,  for  instance,  they  present  only  a  rudimentary 
type,  while  in  the  psittacus  mitratus,  &c,  they  are  wholly  absent; 
they  are  feebly  developed  in  the  emeu,  rhea,  and  cassowary.  When 
these  bones  are  enchylosed  together  at  their  sternal  extremities,  as 
they  ordinarily  are,  they  constitute  a  single  bone,  named  furculum. 
In  the  ostrich  they  do  not  come  in  contact  inferiorly,  although  they 
reach  the  sternum  ;  and  in  the  toucans,  they  neither  come  "in  con- 
tact below,  nor  reach  the  sternum.  It  is  remarkable  that  in  the 
ostrich  they  are  anchylosed  above  with  the  coracoid  and  scapula, 
whilst  almost  in  every  other  species  they  either  continue  separate, 
or  are  movably  jointed  superiorly. 

The  humerus  attains  its  greatest  length  in  the  albatross,  and  is 
shortest  in  the  struthious  birds  and  penguins,  whilst  in  the  swifts 
and  humming  birds  it  is  characterised  by  its  thickness,  strength, 
and  the  development  of  its  muscular  processes.  In  the  cursores  it 
is  short  and  attenuated,  resembling  the  corresponding  part  in  the 
paddle  of  the  turtle.  Its  head  is  oblong  transversely,  and  enlarged 
by  two  lateral  crests,  under  one  of  which  are  to  be  found  the  air 
passages  leading  into  the  bone.  The  lower  extremity  of  the  hu- 
merus is  formed  after  the  manner  of  a  hinge,  consisting  of  an  in- 
ternal spherical  portion  to  articulate  with  the  ulna,  and  an  external 
oblong  portion  for  the  radius. 

The  radius  and  ulna  are  straight  and  slender  bones,  enlarged  at 
their  extremities,  and  placed  one  in  front  of  the  other,  so  as  scarcely 
to  admit  of  any  pronation  or  supination.  In  the  penguins  the  bones 
of  the  fore-arm  are  flattened,  and  articulated  with  the  anterior  edge, 
and  not  the  extremity  of  the  humerus. 

The  carpus  is  composed  of  two  bones  only,  and  so  wedged  in 
between  the  metacarpus  and  fore-arm,  as  to  limit  the  motionsof  the 
hand  to  adduction  and  abduction. 

The  metacarpus  is  chiefly  formed  of  two  bones,  a  small  ulnar 
one,  which  supports  a  single  phalanx,  and  a  large  radial  one,  which 
sustains  two  phalanges.  A  small  rudimental  bone  is  usually  an- 
chylosed to  the  outer  side  of  the  proximal  extremity  of  the  radial 
metacarpal  bone. 

Lower  extremity. — The  pelvic  bones,  like  those  of  the  shoulder, 
are  three  in  number:  the  ilium  represents  the  scapula,  the  ishium 


28  EVERS'S  COMPARATIVE  ANATOMY. 

the  clavicle,  and  the  pubis  the  coracoid  bone.  Unlike  the  shoulder, 
however,  these  bones  are  always  anchylosed  into  one  piece  on 
either  side,  and  with  one  exception,  never  join  in  the  mesial  line ; 
this  single  exception  is  afforded  by  the  ostrich,  in  which  the  pubic 
bones  complete  the  pelvic  circle  by  anchylosing"  at  their  inferior 
extremities.  The  vulture  cinereus,  and  some  acquatic  birds,  form 
the  nearest  approach  to  this  last  condition.  In  them  the  pubic 
bones  are  often  surmounted  by  a  cartilaginous  appendix  at  their 
anterior  extremity. 

The  ilium  is  the  only  bone  of  the  pelvis  that  comes  in  contact 
with  the  spine  ;  it  is  elongated  in  form,  narrow  in  the  centre,  and 
expanded  at  its  extremities.  This  bone  is  anchylosed  with  the 
sacrum,  the  ischium,  and  the  spinous  and  transverse  processes  of 
one  or  two  dorsal  vertebras. 

The  ischium  lies  parallel  with  the  ilium;  it  is  a  small  oblong 
bone,  not  presenting  any  peculiarity. 

The  pubis  unites  with  the  ischium  in  a  two  fold  manner  in  the 
humming  bird  and  some  others,  so  as  to  form  two  foramina  obtura- 
toria,  while  in  others,  as  the  stork,  it  is  only  united  to  it  at  the  coty- 
loid foramen.  This  cavity  is  always  incomplete  at  its  internal  part, 
where  it  is  closed  by  some  fibrous  bands. 

The  femur  is  short,  and  slightly  convex  anteriorly;  its  head  is 
hemispherical,  and  joined  to  the  shaft  at  a  right  angle,  without 
the  intervention  of  a  neck.  There  is  but  one  trochanter;  it  is  of 
a  large  size,  continuous  with  the  external  part  of  the  shaft,  and  gene- 
rally rises  above  the  level  of  the  head.  The  lower  extremity  of 
this  bone  presents  two  condyles,  the  inner  one  for  the  tibia,  the 
outer  one,  which  is  longer  and  larger,  rests  on  the  tibia  and  fibula; 
it  is  convex  from  behind  forwards,  and  terminates  in  a  groove  in 
both  these  directions. 

The  tibia  is  the  principal  bone  of  the  leg,  the  fibula  ending  in  a 
point  inferiorly,  and  achylosed  to  the  tibia  for  a  considerable  extent. 
The  lower  extremity  of  the  tibia  forms  a  transverse  trochlea,  above 
which  there  is  a  deep  groove  or  foramen,  to  transmit  the  tendon  of 
the  extensor  digitorum  communis.  The  upper  and  anterior  part  of 
the  tibia  gives  rise  to  a  long  pointed  process,  which  ascends  in  the 
shape  of  an  olecranon  in  front  of  the  joint,  being  also  anterior  to 
the  patella. 

The  tarsus  can  only  be  recognised  as  a  distinct  segment  of  the 
foot,  when  examined  at  an  early  period  of  the  bird's  existence ; 
then  only  can  be  found  a  distinct  astragalus  of  a  flattened  oval  form, 
convex  superiorly,  and  concave  below,  where  it  meets  the  three 
bones  of  the  metatarsus  partially  separated.  A  rudiment  of  os  calcis 
may  also  be  found  in  the  extensor  tendons.  In  the  penguins,  the 
three  metatarsal  bones  are  only  anchylosed  at  their  extremities ; 
but  in  other  birds,  faint  grooves  alone  indicate  their  existence. 
The  remote  extremity  of  the  metatarsus  presents  three  convex  facets 
to  articulate  with  the  toes.  These  last  are  subject  to  great  variety 
as  to  number,  being  reduced  to  two  in  the  ostrich,  and  increased  to 


VERTEBRATA.  29 

five  in   the  gallinaceae.     The  phalanges  bear  no  proportion  to  the 
size  or  number  of  the  toes,  being  found  to  vary  from  one  up  to  five. 

RECAPITULATION. 

1.  There  is  more  uniformity  observed  in  the  skeleton  of  birds, 
than  in  any  other  of  the  vertebrated  classes. 

2.  The  bones  are  white,  thin,  and  brittle;  in  early  life,  filled 
with  a  thin  serous  oil,  which  is  subsequently  removed  to  be  replaced 
by  atmospheric  air,  especially  in  those  of  the  high-flying  kind. 

3.  The  bones  are  early  and  rapidly  ossified,  particularly  those  of 
the  head,  thorax,  and  pelvis.  This  ossification  also  affects  the  ten- 
dons of  the  muscles  of  the  leg,  sclerotic  tunic  of  the  eye,  inferior 
larynx,  and  the  rings  of  the  trachea. 

4.  Arms  adapted  solely  for  flight ;  legs  for  support. 

5.  Head  and  neck  long,  for  the  purposes  of  prehension. 

6.  The  dorsal  and  sacral  portions  of  the  spine  the  most  fixed. 

7.  Cervical  vertebras  more  numerous  than  in  the  mammalia; 
occasionally,  three  times  the  number. 

MAMMALIA. 

The  number  of  vertebrae  contained  in  the  spine,  is  very  variable ; 
but  the  human  type  is  by  far  the  most  generally  predominant.  In 
the  cetaceae  there  is  no  distinction  between  lumbar,  sacral,  and 
caudal  vertebras  ;  and  in  the  porpesse,  there  are  sixty-six  posterior 
to  the  dorsal :  these  mammalia,  however,  have  no  pelvis.  The 
cervical  vertebrae  are  uniformly  seven  throughout  this  class,  not- 
withstanding Cuvier  imagined  lie  had  found  a  solitary  exception  in 
the  neck  of  the  ai,  bradypus  tridactylus;  but  it  has  been  well  as- 
certained since,  that  what  he  conceived  to  be  the  two  last  cervical 
vertebrae  of  this  animal,  have  two  rudimental  ribs  attached  to  them. 
When  we  are  reminded  of  the  localities  and  habits  of  the  sloth, 
hanging  from  the  branches  of  trees,  and  passing  from  bough  to 
bough,  aided  by  the  current  winds,  it  becomes  obvious  why  such  a 
provision  should  exist,  of  modifying  the  two  superior  dorsal  verte- 
brae, and  of  consigning  to  them  the  offices  of  cervical,  rather  than 
infringe  on  a  law  which  at  present  seems  without  an  exception. 

The  dorsal  vertebrae  range  from  twenty-three,  as  seen  in  the 
unau,  bradypus  didactylus,  to  twelve,  as  presented  by  man,  mice, 
bats,  rabbits,  hares,  and  several  apes.  In  the  megatherium  there 
are  sixteen,  in  the  horse  eighteen,  and  in  the  elephant  twenty. 
The  lumbar  vertebrae  are  generally  seven;  they  vary,  however, 
there  being  two  in  the  two-toed  ant-eater,  and  nine  in  the  lori.  The 
sacral  vertebrae  are  seven  in  the  mole  ;  in  the  vampyre  bat,  opossum, 
and  some  apes,  there  is  but  a  single  sacral  vertebra,  the  usual 
number  being  three.  The  caudal  vertebrae  are  four  in  man  and 
the  ourang-outang;  forty  in  the  two-toed  ant-eater;  and  in  the 
vampire  bat  they  are  altogether  absent. 


30  EVERS'S  COMPARATIVE  ANATOMY. 

In  most  animals,  it  has  been  said,  that  the  head  and  neck  together 
equal  in  length  the  fore-feet,  except  where  the  latter  are  used  as 
hands,  as  in  the  apes  and  rodentia.  The  neck  attains  its  greatest 
length  in  the  genus  cameius,  and  is  shortest  in  the  order  cetacea, 
owing  to  the  consolidation  of  the  vertebrae.  According  to  the 
statement  of  Gore,  the  number  of  cervical  vertebras  in  certain  of 
the  cetacea,  as  the  balaena,  manatee,  and  dugong,  amounts  only  to 
six.  In  the  rodentia,  and  most  long  necked  animals,  the  spinous 
processes  are  almost  wanting.  The  atlas,  in  the  carnivora,  rumi- 
nantia,  solipida,  pachydermata,  <fec,  is  distinguished  by  its  length, 
and  by  its  large  aliform  transverse  processes.  The  free  motion  and 
beautiful  arch  observed  in  the  necks  of  some  horses,  camels,  &c,  is 
explained  by  the  bodies  of  the  cervical  vertebras  having  a  perfect 
articular  head  on  their  upper  surface,  and  a  corresponding  depres- 
sion on  their  lower,  similar  to  what  we  observe  in  the  necks  of 
serpents,  with  this  difference,  that  the  surfaces  are  reversed.  The 
ruminantia,  rhinoceros,  elephant,  &c,  are  remarkable  for  the  great 
length  of  the  spinous  processes  of  the  dorsal  vertebrae.  Bats  have 
scarcely  any  spinous  processes;  and,  with  the  exception  of  the 
second  dorsal,  they  are  short  in  the  rodentia.  In  the  lumbar  ver- 
tebrae, the  form  of  the  transverse  processes  is  very  variable — almost 
absent  in  bats,  very  strong  in  the  ruminantia,  rodentia,  and  carni- 
vora. The  megatherium  possesses  long  spinous  processes.  In  the 
sloth,  the  length,  breadth,  and  consolidation  of  the  sacral  vertebrae 
remind  us  of  the  sacrum  of  birds.  The  few  first  only  of  the  caudal 
vertebrae  in  mammalia  contain  a  prolongation  of  the  vertebral  canal. 
Animals  with  long  movable  tails,  as  the  two-toed  ant-eater,  have 
oblong  triangular  processes  on  the  under  surface  of  the  caudal 
vertebrae,  as  in  the  crocodile.  The  connection  of  the  vertebrae  is 
almost  always  by  means  of  interarticular  cartilage,  as  in  man,  and 
consists  of  concentric  rings,  most  evident  in  the  whale.  In  the 
pig  and  rabbit  the  interarticular  cavities  are  filled  with  an  albu- 
minous fluid,  as  in  fishes. 

Ribs. — Man  has  seven  true  and  five  false  ribs ;  the  balaena 
whale,  one  true  and  eleven  false ;  in  the  unau,  or  two-toed 
sloth,  there  are  twenty-three  pairs,  of  which  eleven  are  false ;  in 
the  horse  eighteen,  and  eight  of  them  false;  in  wolves,  cats,  and 
some  apes,  there  are  thirteen  pairs,  four  of  which  are  false;  in  the 
guinea  pig,  armadillo,  and  porpoise,  there  are  thirteen,  of  which 
seven  are  false ;  in  the  manatee,  of  sixteen  pairs,  but  two  are  true; 
in  the  dugong  but  three  out  of  eighteen  ;  and  in  the  ornithorhynchus 
but  six  out  of  seventeen.  The  breadth  of  the  ribs  is  greater  in  the 
ruminantia,  pachydemata,  in  the  manatee,  and  especially  in  the 
two-toed  ant-eater,  than  in  other  mammalia.  The  connection  of 
the  ribs  with  the  sternum  is  in  general  effected  by  cartilage;  but  in 
the  cetacea,  ant-eaters,  dasypus,  bradypus  man  is,  ornithorhynchus, 
echidna,  and  frequently  in  bats,  the  union  is  completely  bony. 

Sternum. — This  bone,  though  essentially  the  same  as  in  the 
human  subject,  is  somewhat  modified  in  form  by  the  shape  of  the 


VERTEBRATA.  31 

chest.  In  ungulated  animals,  where  there  are  no  clavicles,  the 
sternum-  is  compressed  laterally,  and  projects  in  the  centre  like  a 
ship's  keel.  The  superior  piece  of  the  sternum  is  very  considera- 
ble in  the  mole,  where  it  forms  a  distinct  bone.  It  is  proportionably 
small  in  the  bat,  seal,  horse,  rhinoceros.  In  the  cetacea  it  is 
short  and  large,  being  composed  of  five  pieces  in  the  dugong,  and 
three  in  the  dolphin,  the  porposse,  and  the  platanist.  In  the  bat 
and  ornithorhynchns,  the  upper  part  of  the  sternum  is  T-shaped, 
the  transverse  process  being  for  the  articulation  of  the  clavicle. 

The  figure  of  the  thorax  in  most  apes,  bats,  and  the  greater 
number  of  the  rodentia,  and,  in  fact,  of  the  class  mammalia,  having 
clavicles,  agrees  with  that  of  the  human  subject.  In  ungulated 
animals,  on  the  contrary,  where  there  are  no  clavicles,  the  thorax 
is  laterally  compressed  and  elongated. 

The  whole  arrangement  of  the  thorax  proclaims  man  to  be 
destined  to  move  in  the  erect  attitude:  he  is  the  only  animal  in 
which  its  transverse  exceeds  the  antero-posterior  diameter;  even  in 
the  chimpanse,  which  approaches  nearest  to  him,  the  latter  exceeds 
the  former  measurement,  reminding  us  of  the  form  of  this  cavity 
in  the  very  young  subject.  Its  great  lateral  width  and  inconsider- 
able depth  from  sternum  to  spine,  throw  the  arms  apart,  and  in- 
crease their  sphere  of  motion.  The  reverse  characters,  together 
with  the  absence  of  clavicles  in  quadrupeds,  allow  the  fore  legs  to 
approximate,  to  fall  perpendicularly  under  the  front  of  the  body, 
and  support  it  with  ease  and  security. 

Head. — We  shall  cease  to  wonder  at  the  striking"  differences 
observed  in  the  construction  of  this  part  of  the  skeleton,  when  we 
consider  that  it  forms  the  receptacle  for  the  brain,  most  of  the  ex- 
ternal senses,  the  masticatory  apparatus,  &c.  Man  combines  by 
far  the  largest  cranium  with  the  smallest  face;  and  animals  deviate 
from  these  relations  in  proportion  as  they  increase  in  stupidity  and 
ferocity.  In  man,  the  area  of  the  section  of  the  cranium  is  nearly 
four  times  as  large  as  that  of  the  face;  three  times  as  large 
in  the  ourang-outang;  twice  as  large  in  the  sapajous;  and  they 
are  nearly  equal  in  the  baboons  and  carnivora.  In  the  hare 
and  marmot,  the  face  exceeds  the  cranium  by  one  third;  in  the 
porcupine  and  ruminants,  by  one  half.  The  face  is  three  times 
as  large  as  the  cranium  in  the  hippopotamus,  and  four  times 
as  large  in  the  horse. 

The  superior  maxillary  bones  of  the  human  subject  are  united 
to  each  other,  and  contain  all  the  upper  teeth  ;  in  some  other 
mammalia,  however,  they  are  separated  by  a  coniform  bone,  which 
contains  the  incisor  teeth,  and  hence  named  os  insicivum;  but  it 
exists  where  there  are  no  incisor  teeth,  as  in  the  kerotophara,  the 
elephant,  and  the  two-toed  rhinoceros  of  Africa,  and  even  where 
there  are  no  teeth  at  all,  as  in  the  ant-eater  and  some  of  the  ceta- 
ceans, for  which  reason  Blumenbach  calls  it  os  intermaxillare.  In 
some  it  is  a  single  bone,  in  others  double;  it  is  absent  from  the 
chimpanse,  though  present  in  the  ourang-outang.     The  former  of 


32 

these  animals  possesses  supercilliary  ridges,  which  are  wanting  in 
the  ourang. 

The  head  of  the  ourang,  viewed  in  front,  is  pear-shaped,  expand- 
ing from  the  chin  upwards,  the  cranium  being  much  the  larger 
end.  The  frontal  sinuses  are  very  large  in  the  dog,  wolf,  porcu- 
pine, sloth,  sheep,  bull,  pig,  horse,  and  especially  in  the  elephant; 
they  are  small  in  bats,  rats,  squirrels,  ant-eaters,  the  hippopotamus, 
rhinoceros,  &c.  In  cats,  martens,  and  bears,  the  parietal  bones 
give  off  from  their  inner  and  posterior  edge  a  process  of  bone 
which  projects  into  the  cavity  of  the  skull,  and  forms  a  perfect 
bony  tentorium  cerebelli.  In  the  dog  and  horse,  similar  processes 
arise  from  the  petrous  portion  of  the  temporal  bones. 

The  lower  jaw  is  subject  to  many  varieties  in  the  mammalia. 
In  the  whale  it  resembles  two  enormous  ribs,  united  at  the  point, 
without  any  trace  of  ascending  rami  or  coronoid  processes.  The 
articular  head  here,  as  well  as  in  the  porpoise,  is  directed  back- 
wards, and  is  attached  to  the  skull  by  means  of  strong  cellular 
tissue,  filled  with  oil. 

In  the  hare,  rabbit,  and  guinea-pig,  of  the  order  rodentia,  the 
coronoid  process  is  very  small;  in  others,  as  squirrels  and  rats,  it 
is  pretty  large.  The  condyloid,  or  articular  process,  is  compressed 
latterally,  directed  from  behind  forwards,  and  larger  in  front  than 
behind. 

In  the  carnivora,  the  articular  head  is  directed  transversely,  and 
so  closely  adapted  to  the  glenoid  cavity  of  the  temporal  bone  that 
the  jaw  retains  its  situation  after  the  destruction  of  the  ligaments. 
This  is  well  seen  in  the  marten  and  sea-otter.  In  the  ruminants 
the  condyle  is  very  flat,  to  admit  of  the  lateral  motion  necessary 
during  the  process  of  rumination.  In  the  carnivora,  rodentia,  and 
ruminantia,  the  two  halves  of  the  lower  jaw  are  never  firmly 
united — in  this  particular  affording  us  an  instance  of  the  perma- 
nence of  a  condition  in  other  mammalia,  which  in  man  is  peculiar 
to  the  earliest  periods  of  life. 

Swine  have  two  small  bones  placed  at  the  aterior  openings  of 
the  nares  for  the  support  of  the  snout.  In  fine,  it  is  to  be  remarked 
that  the  crania  of  all  the  quadrumana,  together  with  the  other 
mammalia,  are  distinguished  by  the  comparative  size,  great'length 
and  projection  of  the  jaws. 

Anterior  extremity. — This  extremity  in  the  lower  animals  cor- 
responds to  the  superior  of  the  human  subject,  and  contains  all 
the  elements  of  it.  modified  according  to  the  habits  of  the  animal. 
Sometimes  connected  to  the  trunk  by  means  of  muscle  only,  as  in 
the  cetacea,  pachydermata,  ruminantia,  and  solipe  a;  in  other  in- 
stances by  ligament  and  muscle,  as  seen  in  the  insectivora. 

Clavicle. — The  importance  of  this  bone,  in  the  motions  of  the 
upper  or  anterior  extremity,  may  be  well  estimated  by  the  fact  of 
its  being  present  in  those  animals  only  whose  habits  of  life  require 
free  and  varied  motions  of  the  shoulder.  Thus  in  the  quadrumana 
it  is  strong  and  curved,  as  in  the  human  subject.     The  bat,  hedge- 


VERTEBRATA.  33 

hog,  and  mole,  among  the  insectivora,  afford  examples  of  clavicle 
in  its  highest  degree  of  development.  It  is  very  perfect  in  the 
rodentia,  as  the  squirrel,  beaver,  rabbit,  rat,  &c.  Among  the  eden- 
tata,  those  animals  only  whose  habits  are  fossorial  possess  clavicle, 
as  the  ant-eater,  the  dasypus,  and  the  gigantic  megatherium  ;  in 
the  last  named  animal  it  presents  the  peculiarity  of  being  articulated 
with  the  first  rib  instead  of  the  sternum. 

Where  the  anterior  extremity  is  employed  merely  for  the  purpose 
of  progression,  we  find  no  clavicle,  as  in  the  pachydermata,  rumi- 
nant ia,  cetacea,  and  solipeda.  In  the  carnivora.  where  there  is  a 
slight  increase  in  the  range  of  motion  of  the  anterior  extremities, 
the  clavicle  exists  in  a  rudimental  form,  and  its  development  is  in 
proportion  to  the  motion  enjoyed  ;  hence  it  is  small  and  short  in 
the  cat,  the  bear,  and  the  dog ;  in  those  animals  it  has  no  attachment 
to  the  sternum  or  scapula,  but  lies  loose  among  the  muscles. 

Scapula. — This  bone  forms  an  essential  element  of  the  thoracic 
extremity,  and  exists  wherever  the  latter  is  fully  developed,  but 
greatly  modified,  according  to  the  uses  to  winch  the  extremity  is 
applied.  The  cetacea,  in  general,  have  a  large  scapula  of  a  trian- 
gular form;  the  pachydermata,  ruminantia,  and  solipeda,  have  a 
long  narrow  scapula  placed  perpendicularly  on  the  anterior  and 
lateral  part  of  the  chest.  In  the  carnivora  and  rodentia,  where 
strength  and  freedom  of  motion  are  required,  the  scapulas  are  placed 
obliquely  over  the  ribs;  and  it  is  interesting  to  observe  how  the 
obliquity  of  the  glenoid  cavity  varies  with  the  motions  required. 
This  fact  has  not  escaped  the  observation  of  the  horse-jockey,  who 
is  well  aware  that  the  upright  shoulder  is  the  mark  of  a  stumbling 
horse. 

Humerus. — When  the  fore-arm  and  hand  are  used  for  seizing 
objects,  as  in  apes,  many  rodentia  and  carnivora,  or  for  flying,  as 
in  the  bat,  the  humerus  is  formed  essentially  in  accordance  with 
the  human  type.  On  the  contrary,  when  the  anterior  part  of  the 
member  is  but  slightly  developed,  as  in  the  cetacea,  the  bone  is 
short  and  thick;  and  in  the  whalebone  whale,  it  is  nearly  as  broad 
as  it  is  long.  In  the  mole  it  is  short,  thick,  and  strong;  its  tuber- 
osities greatly  developed,  and  its  upper  extremity  presents  two  arti- 
culating surfaces,  one  for  the  scapula,  and  the  other  for  the  clavicle. 
This  large  size  of  the  bone  prevails  in  all  the  other  fossorial  ani- 
mals, as  the  mighty  megatherium,  the  pangolins,  beavers,  ant-eaters, 
and  monotremata.  The  humerus  of  the  lion  is  remarkable  for 
being  perforated  by  the  brachial  artery  and  nerve,  in  order  to  avoid 
being  crushed  by  the  huge  and  powerful  mass  of  muscles  exhibited 
in  this  part  of  the  economy  of  the  king  of  beasts. 

Fore-arm. — The  radius  and  ulna  are  very  short  in  the  cetaceans, 
and  in  most  of  them  consolidated  too-ether  at  both  extremities.  In 
the  cheiroptera  they  are  long,  slender,  and  firmly  united,  to  accord 
with  their  mode  of  progression  by  flight;  in  some  the  olecranon  is 
wholly  absent,  and  in  others,  as  the  vampyre,  it  exists  in  the  form 
of  a  patella.  The  ruminants  and  solipeds  have  these  bones  con- 
7 — ff  cvers  3 


34 

solidafed  into  one.  The  rodentia,  many  carnivora,  pachydermata, 
insectivora,  and  edentata,  the  bones  are  distinct  throughout,  but 
admit  of  no  motion.  The  sloth,  however,  among  the  edentata, 
enjoys  great  freedom  of  pronation  and  supination ;  here  the  bones 
are  long,  arched,  and  widely  separated  in  the  centre. 

Carpus. — The  bones  composing  this  part  of  the  extremity  are 
usually  disposed  in  two  rows,  as  in  man.  though  the  number  almost 
invariably  differs  from  that  model.  The  following  is  Cuvier's 
statement  of  their  number: — In  man  and  the  elephant.  8;  in  apes, 
the  hare,  and  the  mole,  9:  in  the  solipeda,  carnivora  and  several 
rodentia,  7 ;  in  the  ruminantia  from  6  to  7 ;  in  the  edentata,  6;  and 
in  cetacea  from  4  to  7.  In  apes,  carnivora,  and  several  of  the  un- 
gulata,  the  pisciform  bone  is  very  large,  and  by  affording  attachment 
to  the  flexor  muscles  of  the  hand,  performs  the  office  of  os  calcis 
in  the  foot.  The  simise,  in  general,  have  nine  bones  in  the  carpus — 
another  distinction  between  their  hand  and  that  of  man.  In  the 
most  anthropo-morphous  of  them,  the  chimpanse  and  the  ourang- 
outang,  the  ninth  is  a  sesamoid  bone  in  the  tendon  of  the  abductor 
pollicis  longus. 

The  metacarpal  bones  in  the  whale  are  five  in  number  and 
flattened  in  the  form  of  phalanges.  These  last  are,  two  in  the 
thumb,  three  in  the  little  finger,  four  in  the  index  and  ring  fingers, 
and  five  in  the  middle,  collectively  forming  a  short  but  strong 
paddle.  The  shovel-shaped  hand  of  the  mole  consists  of  five  fingers, 
each  having  a  metacarpal  bone  and  three  phalanges.  In  the 
bat  the  thumb  is  short,  and  not  included  within  the  flying  membrane, 
The  metacarpal  bones  are  long,  slender,  and  cylindrical :  the  distal 
phalanx  is  hooked,  and  sustains  a  nail  by  which  the  animal  suspends 
itself.  The  simias  have  these  parts  constructed  as  in  man,  except 
the  thumb,  which  is  small,  and  extends  only  to  the  metacarpopha- 
langeal articulation.  In  bears  and  badgers  the  five  fingers  are  of 
equal  length,  and  parallel  to  each  other.  In  the  endentata  several 
of  the  fingers  disappear;  for  instance  in  the  two-toed  ant-eater,  the 
thumb,  index,  and  little  fingers,  are  merely  rudimentary;  the 
middle  finger,  however,  is  proportionally  developed. 

Among  the  ungulata  the  hand  is  still  more  diversified  ;  the  ele- 
phant, for  example  has  five  fingers  all  united  into  one  mass  within 
the  skin.  The  pig  almost  wants  the  thumb;  he,  however,  has  four 
perfect  fingers,  but  walks  only  on  two.  The  ruminantia  have  but 
two  fingers,  each  metacarpal  bone  supporting  three  phalanges.  In 
the  solipeda  there  is  but  a  single  finger;  for  instance,  in  the  horse 
the  carpus  corresponds  to  the  knee ;  the  metacarpal  bones  are  con- 
solidated into  one,  cannon  bone,  behind  which  there  are  two  small, 
splint  bones,  commencing  broad  at  the  knee,  and  terminating  in  a 
pointed  manner  behind  the  lower  third  of  the  cannon  bone.  Here 
we  meet  with  three  phalanges,  the  first  called  pastern,  the  second 
coronet,  and  the  third  coffin  bone. 

Pelvis. — It  has  been  truly  asserted  that  in  the  human  skeleton 
alone,  a  true  pelvis  is  to  be  found.     This  arises  from  the  form  and 


VERTEBRATA.  35 

manner  of  connection  of  the  bones  entering  into  the  formation  of 
this  cavity.  The  chimpanse  and  elephant  afford  ns  the  nearest 
approach  to  the  human  formation,  even  here  the  ilia  are  narrow 
and  elongated  ;  and  the  sacrum  and  coccyx  are  flat,  contracted,  and 
continued  in  a  direct  line  with  the  spine.  Next  in  the  order  of 
development  may  be  ranked  the  rhinoceros,  the  ox,  the  horse,  the 
carnivora  and  the  rodentia.  In  ant-eaters,  moles,  and  shrews,  the 
symphysis  pubis  remains  open;  and  in  the  two  latter  genera  the 
pelvis  is  so  small  that  the  pelvic  viscera  are  placed  without  it.  The 
megatherium  and  sloth,  however,  have  pelvis  of  large  dimensions. 
Some  of  the  edentata,  as  the  dasypus,  have  the  ilia  joined  to  the 
sacrum.  In  others,  as  the  sloth  and  some  of  the  ant-eaters,  the 
ischium  is  connected  with  the  sacrum,  forming  an  ischiatic  foramen, 
instead  of  a  notch.  The  cetacea  present  but  slight  rudiments  of  a 
pelvis  in  the  form  of  two  small  bones  united  to  each  other  and  to 
one  of  the  vertebrae  by  cartilage.  Finally  the  marsupial  animals 
present  a  small,  elongated  pelvis,  especially  remarkable  for  the  pre- 
sence of  two  particular  bones  not  found  in  any  other  mammiferous 
animal  even  in  a  rudimental  state,  and  named  0.95a  marcip'ialia. 
These  bones  are  attached,  but  not  articulated,  to  the  anterior  part 
of  the  pubis,  near  the  symphysis;  each  is  about  three  inches  long 
in  the  kangaroo,  flat,  with  anterior  thin,  and  a  posterior  thick 
edge.  The  bone  is  triangular  in  form,  the  broad  end  being  at  the 
pubis,  while  the  narrow  has  attached  to  it  the  abdominal  muscles. 
The  use  of  these  bones  is  to  support  the  marsupium,  or  abdo- 
minal pouch,  in  which  the  mammary  apparatus  is  lodged,  and  the 
young  animal  nurtured. 

The  posterior  or  abdominal  extremity  is  altogether  absent  in 
the  cetacea.  In  the  other  mammalia  inhabiting  the  sea,  the  seal, 
for  instance,  the  several  elements  of  the  posterior  extremity,  even 
the  toe-nails,  are  distinctly  recognisable,  but  consolidated  by  a 
membranous  web  into  a  kind  of  caudal  fin. 

The  femur  in  the  lower  mammalia  is  short  and  straight ;  the 
neck  is  either  absent  or  but  little  developed,  the  head  being  placed 
vertically  over  the  shaft.  The  trochanters  and  linea  aspera  are 
badly  marked.  This  bone  is  shorter  than  the  tibia,  the  converse  to 
what  obtains  in  man.  In  the  megatherium  its  thickness  equals 
half  its  length.  The  trochlea  is  a  deeper  and  the  transverse 
diameter  of  the  condyles  less  than  in  man. 

The  patella  is  usually  present  in  the  mammalia;  best  developed 
in  the  pachyderms,  solipeds,  and  monotrems;  least  so  in  the  carni- 
vora and  quadrumana;  and  wholly  absent  in  the  marsupiata  and 
cheiroptera. 

Tibia  and  Fibula. — Throughout  the  mammalia  these  bones 
coincide  pretty  nearly  with  those  of  the  fore-arm.  As  in  man,  the 
tibia  forms  the  chief  bone  of  the  leg.  The  fibula  is  analogous  to 
the  ulna,  and  is  found  only  in  a  rudimentary  state  in  the  solipeds 
and  ruminants,  as  the  latter  bone  was  in  these  animals.  In  the 
solipeds,  the  fibula  is  applied  to  nearly  the  upper  half  of  the  outer 
surface  of  the  tibia,  being  pretty  large  above,  and  ending  in  a  fine 


36  EVERS'S  COMPARATIVE  ANATOMY. 

point  below.  Ruminants,  on  the  contrary  have  the  fibula  better 
developed  inferiorly  where  it  forms  the  external  malleolus  and  ex- 
tends but  a  short  way  up  the  leg.  Pachyderms,  and  all  the  ungili- 
Gulata,  possess  a  fibula  well  developed  ;  and  in  sloths  its  lower 
extremity  ends  in  a  conical  point,  which  enters  a  corresponding 
cavity  in  the  astragalus.  In  the  rodentia,  and  insectivora,  particu- 
larly the  mole,  the  tibia  and  fibula  are  united  through  their  inferior 
half.  Carnivora  have  these  bones  fully  developed  and  detached: 
this  is  well  seen  in  the  phocidee  and  felina?.  In  the  dog  they  are 
united  posteriorly. 

Tarsus. — The  bones  composing  this  part  of  the  foot  for  the 
greater  part  resemble  those  of  man.  The  cheiroptera  present  a 
remarkable  peculiarity  in  the  formation  of  a  long  slender  bone, 
extending  from  the  back  of  the  os  calcis  half  way  to  the  tail,  and 
enclosed  within  the  flying  membrane.  Cuvier  and  Meckel  supposed 
it  to  be  a  portion  of  the  os  calcis,  whilst  Daubeton  conceived  it  to 
be  a  distinct  bone.  On  the  inner  side  of  the  tarsus  of  the  mole,  a 
sickle-like  process  of  bone  is  found,  similar  to  that  observed  on  the 
carpus.  The  metatarsus  and  toes  in  ruminants  and  solipeds  are 
disposed  pretty  nearly  as  in  the  anterior  extremities.  The  rodentia 
and  carnivora  have  usually  five  toes,  the  great  one  being  often 
shortened,  or  as  in  cats,  dogs,  and  hares,  altogether  absent.  The 
quadrumana  and  marsupiales  have  the  great  toe  separated  from  the 
rest,  bearing  the  same  relation  to  the  foot  as  the  thumb  to  the  hand. 

Although  the  disproportion  in  the  respective  size  and  length  of 
the  upper  and  lower  extremities  of  the  human  subject,  indicate  the 
different  functions  they  are  designed  to  execute,  yet  they  present 
many  similarities  throughout  their  divisions,  the  construction  of 
their  articulations,  and  the  number  and  form  of  their  bones.  The 
arm,  fore-arm,  and  hand,  lor  instance,  resemble  the  thigh,  leg,  and 
foot;  the  os  innominatum  may  be  compared  to  the  scapula;  the 
hip,  knee,  and  ankle,  to  the  shoulder,  elbow,  and  wrist:  and  the 
carpus,  metacarpus,  and  fingers,  to  the  tarsus,  metatarsus,  and  toes. 
Contrast. — A  line  falling  perpendicularly  from  the  shoulder  in  the 
erect  attitude,  would  pass  behind  the  hip.  The  upper  extremities 
diverge  below,  whilst  the  inferior  converge.  The  deep  acetabulum, 
and  the  strong  tight  capsule  of  the  hip,  may  be  well  contrasted 
with  the  shallow  glenoid  cavity,  and  weak,  loose  capsule  of  the 
shoulder.  The  lower  extremities  are  as  long  as  the  head  and 
trunk  together,  being  only  equaled  in  this  respect  by  the  kangaroo 
and  jerboa. 

The  great  length  of  the  shaft  and  neck  of  the  femur,  its  perpen- 
dicularity with  the  spine,  and  the  depth  of  its  internal  condyle,  are 
characters  peculiar  to  man  :  in  the  fore-arm  every  thing  conspires 
to  procure  freedom  of  motion;  in  the  leg,  strength  and  security  are 
the  objects  aimed  at.  The  hand  is  articulated  on  a  line  with  the 
fore-arm,  and  enjoys  free  and  varied  motions;  the  leg  joins  the 
foot  at  a  right  angle,  and  moves  chiefly  in  the  angular  direction; 
the  entire  surface  of  the  tarsus,  metatarsus,  and  toes,  rests  on  the 
ground :  the  two  latter  circumstances  are  exclusively  confined  to 


VERTEBRATA.  37 

the  human  subject.  The  parts  composing  the  hand  and  foot  are 
disposed  inversely  as  regards  their  development  and  importance. 
The  solid  part  of  the  hand  is  small,  weak,  and  but  slightly  deve- 
loped ;  that  of  the  foot  is  large,  firm,  and  ossified  at  an  earlier 
period  of  life.  The  fingers  are  long,  slender,  and  mobile;  the  toes 
are  short,  thick,  and  enjoy  only  a  limited  share  of  motion.  But  the 
distinguishing  characteristic  of  the  human  hand  is  due  to  the 
strength,  situation,  and  development  of  the  thumb,  which  is  oppos- 
able to  the  fingers,  and  rendered  useful  in  the  thousand  offices 
which  it  has  been  designed  to  execute. 

Man  is  distinguished  from  all  other  animals  by  the  great  size  of 
the  cranium  over  that  of  the  face.  One  method  of  expressing 
these  relative  proportions,  is  by  the  course  of  the  facial  line,  and 
the  number  of  degrees  in  the  facial  angle.  A  line  drawn  from  the 
greatest  prominence  of  the  forehead  to  that  of  the  upper  maxillary 
bone,  in  the  erect  attitude,  describes  the  direction  of  the  face,  and 
is  called  the  facial  line ;  a  second  line,  perfectly  horizontal,  drawn 
backwards  from  beneath  the  basis  of  the  nostrils,  forms  with  the 
other  what  is  termed  the  facial  angle,  and  gives  the  measure  of 
the  relative  prominence  of  the  jaws  and  forehead.  In  the  adult 
human  subject  the  facial  angle  varies  from  65°  to  85°;  in  children 
it  reaches  90°;  a  sufficient  proof  of  its  inadequacy  as  a  standard 
for  the  measurement  of  intellect.  The  situation  of  the  foramen 
magnum,  and  occipital  condyles,  being  but  little  posterior  to  the 
centre  of  gravity,  are  also  distinctive  characters  of  man.  Aline 
drawn  forwards  parallel  to  the  plane  of  the  foramen  magnum,  will 
come  out  just  under  the  orbits.  In  the  ourang-outang  this  line 
would  pass  below  the  level  of  the  lower  jaw,  and  in  most  other 
animals  the  foraman  magnum  is  placed  on  the  back  of  the  head, 
its  plane  being  nearly  vertical.  The  great  weight  of  the  human 
head,  the  absence  of  ligamentum  nuchas,  and  of  the  rete  mirabile, 
or  some  analogous  provision  for  moderating  the  influx  of  blood  to 
the  brain,  coupled  with  other  facts  hereafter  to  be  mentioned,  in- 
contestably  prove  that  man  was  intended  for  the  erect  attitude,  and 
that  he  is  quite  unfit  to  move  on  all-fours,  as  some  modern  authors 
would  have  it. 

Nature  has  clad  in  defensive  mail  the  armed  rhinoceros,  provided 
the  lion  and  the  ti^er  with  weapons  of  defence,  clothed  the  sheep 
in  wool,  and  the  bear  in  fur;  every  animal  she  has  bountifully 
provided  in  all  that  was  necessary  for  its  subsistence,  and  adapted 
to  its  destined  mode  of  existence.  Man  alone  she  has  abandoned, 
weak,  naked,  and  defenceless,  unarmed  in  the  midst  of  dangers, 
and  uncovered  to  the  winds  of  heaven.  But  she  has  bestowed  on 
him  gifts  far  more  than  equivalent  to  all  that  was  denied:  she  has 
given  him  an  illimitable  capacity  for  improvement;  she  has  endowed 
him  with  terrestrial  ubiquity,  or  a  capability  of  inhabiting  every  part 
of  the  known  world:  and  above  all,  she  has  conferred  on  him  in- 
tellect and  inventive  genius,  which  have  raised  him  to  a  measure- 
less superiority  over  the  rest  of  created  beings.  By  means  of  these 
endowments  he  has  made  most  animals  subservient  to  his  purposes, 


3S 

and  obedient  to  his  commands ;  and  such  as  their  native  ferocity- 
renders  incapable  of  utility,  or  dangerous  to  Ii is  repose,  he  has 
banished  to  the  "howling  wilderness."  In  fine,  the  surface  of  the 
earth  attests  his  industry  and  intelligence,  and  nature  herself  is 
delighted  to  obey  him. 

Recapitulation. — Characters  Peculiar  to  Man. 

Biped  ;  bimanous ;  erect  attitude  ;  great  proportion  in  the  size 
of  the  cranium  over  that  of  the  face;  development  of  brain  ;  direc- 
tion of  facial  line;  articulation  of  the  head  with  the  spine;  rational; 
endowed  with  speech  ;  prominent  chin,  and  teeth  of  peculiar  cha- 
racters;  absence  of  ligamentum  nuchas  and  intermaxillary  bone: 
great  transverse  measurement  of  the  chest;  curved  spine,  sacrum, 
and  coccyx;  large  pelvis;  short  arms;  long,  powerful  thumb,  pos- 
sessing separate  flexors ;  length  and  direction  of  the  neck  of  the 
femur  ;  depth  of  internal  condyle  ;  the  whole  flat  of  the  foot  resting 
on  the  ground,  and  the  leg  joining  it  at  a  right  angle.  Man  is  also 
remarkable  for  the  smoothness  of  his  skin,  and  the  slowness  of  his 
growth. 

The  following  are  Camper's  measurements  of  an  ourang-outang, 
compared  with  those  of  man  : 


MAN. 

OURANG 

Whole  length  of  the 

body 

from  vertex  to  heel 

i 

71  inches. 

Less  than  30    ii 

ic\ 

Superior  extremity. 

32      " 

a 

24| 

a 

Inferior         do. 

39      " 

a 

16 

a 

Humerus, 

13      " 

ii 

81 

a 

Ulna, 

91    " 

ii 

9 

a 

Hand, 

8*    " 

ii 

7 

a 

Thumb, 

4i    " 

ii 

« 

a 

Middle  finger, 

41     M 

ii 

3 

a 

Femur, 

20      " 

ii 

7 

a 

Tibia, 

16|    " 

ii 

7 

a 

Foot, 

10i    " 

ii 

n 

a 

Middle  toe, 

2\    " 

a 

2k 

a 

FOSSIL  BONES  OF  ANIMALS. 

It  is  the  undivided  opinion  of  geologists,  that  there  has  been  a 
regular  succession  of  deposits  in  the  earth,  and  that  the  remains  of 
different  animals  (many  of  them  long  since  extinct)  are  to  be  found 
in  the  several  strata.  In  the  deeper  strata,  the  remains  of  animals 
low  in  the  scale  of  organisation  are  to  be  met  with  ;  in  higher 
strata,  oviparous  animals  of  large  size  and  complex  structure  are 
discovered;  above  these  are  found  mammalia;  and  still  nearer  to 
the  surface,  the  bones  of  the  megatherium,  mastodon,  rhinoceros, 
elephant,  &c. ;  and  it  is  now  the  prevalent  opinion  that  man  was 
created  last  of  all. 


LIGAMENTS.  39 

Some  bones  are  found  with  their  animal  ingredients  remaining 
others  are  fossilised.  The  phosphate  of  lime  loses  its  phosphoric 
acid,  and  the  earth  remains  incorruptible,  while  the  soft  animal 
matter  decomposes  and  dissipates.  The  bone  in  this  condition 
may  become  fossilised  ;  silicious  earth,  or  lime  combined  with  iron, 
may  pass,  by  infiltration,  into  the  interstices  of  the  original  earthy 
matter,  and  in  this  state  it  is  permanent  as  the  solid  rock. 

There  is  preserved  in  the  Royal  Museum  of  Madrid,  a  skeleton 
of  the  enormous  megatherium  of  Cuvier.  It  is  supposed  that  the 
animal  was  seven  feet  in  height;  for  its  femur  is  three  times  the 
diameter,  and  its  pelvis  twice  the  breadth  of  that  of  an  elephant. 


CHAPTER  IV. 

LIGAMENTS. 

In  the  lowest  grades  of  animal  beings,  cartilages,  synovial  mem- 
branes, capsular  or  accessary  ligaments,  scarcely  exist  at  the  joints. 
We  here  rind  the  movable  points  formed  of  a  tough  connecting 
material,  which,  by  its  elasticity,  admits  of  the  limited  motions 
required. 

No  ligamentary  apparatus  appears  in  the  soft,  gelatinous  animal- 
cules ;  but  the  silicious  and  calcareous  spicula  of  the  poripherous 
radiata  are  supported  by  a  tough,  elastic  species  of  cellular  tissue. 
The  plates  composing  the  shells  of  the  echinida  are  united  by 
sutures,  and  the  enarthroidal  joints  of  the  spine  by  capsules,  and 
often  by  a  ligamentum  teres,  as  in  the  cidaris.  In  the  larger  Crus- 
tacea and  coleopterous  insects  portions  of  the  skeleton  are  locked 
into  each  other,  where  they  move  securely,  but  to  a  limited  extent, 
in  the  angular  direction  without  ligaments.  The  shells  of  the  con- 
chifera  are  united  by  their  locking  teeth,  and  by  a  strong,  tough 
ligament,  which,  by  its  elasticity,  constantly  tends  to  the  separation 
of  the  bivalves. 

In  the  soft,  flexible  skeletons  of  the  cartilaginous  fishes,  the  liga- 
ments are  few,  and  confined  to  the  organs  for  mastication  and  pro- 
gressive motion.  But  in  the  osseous  fishes  the  ligaments  of  the 
spine  are  white,  fibrous,  dense,  and  highly  elastic  ;  and  here,  for  the 
first  time,  we  meet  the  contiguous  ends  of  bones  incrusted  with  car- 
tilage. In  the  amphibia,  and  in  the  reptiles,  the  bodies  of  the  vertebrae 
are  united  by  enarthroses,  furnished  with  strong  fibrous  capsules  and 
synovial  secretion.  Here  we  have  external  fibrous  bands,  inter- 
spinous  ligaments,  and  occasionally  loose  cartilages  in  the  joints. 
The  capsular  ligaments  of  birds  are  thin  and  strong :  their  cartilages 
of  incrustation  are  also  thin,  but  their  joints  are  freely  supplied 
with  synovia  and  their  hip  joint  furnished  with  a  strong  ligamen- 
tum  teres. 


40  EVERS's  COMPARATIVE  ANATOMY. 

In  the  mammalia,  thick  fibro-cartilages  appear  interposed  between 
the  bodies  of  the  vertebras,  and  in  the  carnassier  and  climbing 
mammalia,  the  articular  processes  are  furnished  with  well  developed 
synovial  capsules.  The  tails  of  many  quadrupeds  enjoy  full  motion 
from  their  coccygeal  vertebras  being  united  by  synovial  capsules. 
The  anterior  and  posterior  common  ligaments  of  the  spine  are 
powerfully  strong  and  highly  elastic  along  the  pliant  columns  of 
the  cetacea.  In  the  large  and  heavy-headed  herbivorous  quadru- 
peds, the  ligamentous  nuchas  is  of  great  size  and  strength,  extending 
from  the  occipital  protuberance  along  the  cervical  and  dorsal  spines, 
and  in  many  instances,  to  the  coccygeal  and  iliac  spines.  The 
light-headed,  and  active  muscular  carnassier  have  this  ligament 
short  and  small,  and  in  the  quadrumana  and  many  of  the  rodentia 
scarcely  a  trace  of  it  is  to  be  found.  The  inter-articular  cartilage 
of  the  lower  jaw  is  met  with,  in  this,  but  not  in  the  preceding  classes, 
the  ligamentum  teres  is  found  in  most  of  this  class,  but  is  said  to  be 
absent  from  the  ourangs,  the  elephant,  the  rhinoceros,  the  hippopo- 
tamus, the  kangaroo,  the  sloths,  and  the  monotremata.  The  two 
toes  of  those  ruminants,  whose  habits  oblige  them  to  make  rapid 
and  bounding  movements,  are  secured  by  strong  transverse  liga- 
ments passing  between  their  phalanges. 


CHAPTER  Y. 

ON  THE  MUSCULAR  SYSTEM  IN  THE  INVERTEBRATA. 

General  observations. — In  the  higher  orders  of  animals,  there  is 
a  close  relation,  and  a  perfect  mutual  dependence  between  the 
osseous  and  the  muscular  systems;  so  much  so,  indeed,  that  the 
arrangement  of  one  may  be  at  once  inferred  by  any  one  who  pos- 
sesses a  sufficient  acquaintance  with  the  other.  It  is  by  means  of 
this  system  that  animals  are  enabled  to  move  from  place  to  place,  to 
seize,  masticate,  and  swallow  their  aliment,  to  circulate  their  fluids, 
to  expel  their  excretions,  to  produce  various  sounds,  and  to  accom- 
plish an  infinitude  of  other  purposes.  A  system  ordained  to  execute 
so  many  offices  cannot  fail  to  present  some  interesting  peculiarities 
in  the  animal  kingdom.  In  obedience  to  a  law,  often  alluded  to, 
we  find  that  the  muscles  of  the  highest  classes  of  red-blooded  ani- 
mals, during  their  development,  pass  through  the  soft,  colourless, 
and  gelatinous  condition  of  those  of  the  lowest  species  before  they 
attain  the  characters  peculiar  to  them  in  their  highest  state  of 
development. 

Radlata. — No  muscular  fibres  have  been  hitherto  found  in  the 
polygastric  animalcules.  Their  rapid  motions  through  the  fluids 
which  they  inhabit  appear  to  be  accomplished  by  means  of  the  vibra- 
tions of  minute  cilia  (which  are  analogous  to  the  villi  on  the  mucous 
surface  of  a  small  intestine)  growing  from  the  outer  surface  of  their 


MUSCULAR  SYSTEM  OF  THE  INVERTEBRATA.  41 

bodies  ;  the  cilia  which  in  these  animalcules,  serve  the  double  pur- 
pose of  locomotive  and  respiratory  organs,  have  been  observed  in 
every  class  of  animals,  even  the  mammalia. 

In  the  zoophytes,  the  soft,  fleshy  mass,  which  we  have  seen 
secrete  the  solid  matter  of  the  skeleton,  possesses  distinct,  but  lan- 
guid irritability:  no  part  of  these  animals  is,  however,  so  irritable 
and  contractile  as  their  prehensile  sacs  or  polypi.  It  is  not  till  we 
arrive  at  the  stellerida  and  asterias  that  distinct  muscular  fibres 
have  been  satisfactorily  demonstrated  ;  and  in  the  echinida  strong 
adductor  and  abductor  muscles  are  seen  attached  to,  and  moving  the 
jaws  of  several  species. 

Articulata. — Seeing  that  these  animals  possess  an  extensive  sur- 
face for  respiration,  and  a  highly  developed  nervous  system,  we  are 
prepared  to  meet  with  considerable  muscular  energy.  Accordingly, 
in  the  nematoid  entozoa,  strong  muscular  fibres  are  seen  taking 
different  directions:  the  rotiferous  or  wheel-animals,  are  also  re- 
markable for  the  development  of  the  muscular  apparatus  provided 
for  the  movements  of  their  jaws,  and  long  vibratile  cilia.  The 
common  earth  worm  has  distinct  muscles  appropriated  to  the  move- 
ments of  its  conical  pointed  feet,  and  its  anus  is  well  furnished  with 
levator  and  sphincter  muscles.  The  insects  and  the  air-breathing 
arachnida  possess  a  well  marked  muscular  system  ;  but  of  all  the 
branchiated  invertebrata,  the  Crustacea  possess  the  largest  proportion 
of  muscle  ;  this  they  require  for  the  purpose  of  swimming,  escaping 
from  danger,  &c.  Although  these  animals  are  provided  with  ex- 
ternal organs  of  mastication,  the  interior  of  their  stomach  is  set 
with  numerous  teeth,  and  its  exterior  provided  with  a  suitable 
arrangement  of  muscle. 

Mollusca. — The  muscular  system  presents  much  greater  variety 
of  form  in  this  than  in  the  articulate  class.  The  tunicata  possess 
a  distinct  muscular  coat  within  their  cartilaginous  covering,  by 
which  they  act  on  their  entire  body,  and  empty  their  thoracic 
cavity;  the  orifice  of  which,  as  well  as  the  anus,  is  provided  with 
sphinctorial  muscles.  The  foot  of  the  conchifera,  by  which  they 
swim,  creep,  burrow,  or  attach  themselves,  is  hollow,  and  composed 
almost  entirely  of  muscular  fibres,  taking  different  directions.  This 
foot  occasionally  admits  the  water  into  its  interior,  and  is  absent 
from  the  oyster  and  others  where  the  shell  is  permanently  fixed. 
In  the  gasteropoda,  the  foot  is  the  largest  muscle  in  the  body,  and 
in  trachelipodous  gasteropods  or  those  residing  in  turbinated  shells, 
its  fibres  are  traceable  up  to  the  neck,  and  backwards  to  be  attached 
to  the  shell.  The  predaceous  gasteropods  possess  a  powerful  mus- 
cular proboscis  provided  with  a  fleshy  tongue,  armed  with  sharp 
conical  teeth,  as  seen  in  the  common  whelk,  (buccinum  undatum.) 
In  the  chephalopoda  and  pteropoda,  muscular  fins  are  attached  to 
the  side  of  the  trunk  for  progressive  motion.  And  in  the  naked 
cephalopods,  a  thin  panniculus  carnosus  with  interlacing  fibres,  is 
spread  all  over  the  body,  beneath  the  coloured  skin  of  the  mantle. 
The  octopus  is  destitute  of  any  lateral  fins,  but  is  provided  with  a 


42 

muscular  membrane  extended  between  the  bases  of  its  feet,  by 
which  it  is  enabled  to  swim  ;  but  what  is  curious  about  it  is,  that 
it  swims  backwards  by  impelling  the  water  forwards. 


CHAPTER  VI. 

ON  THE  MUSCULAR  SYSTEM  IN  THE  VERTEBRATA. 
PISCES. 

In  all  the  vertebrata  the  soft  parts  are  uniformly  placed  external 
to  the  hard  resisting  textures  :  in  them  the  muscles  of  animal  life 
are  generally  of  a  red  colour,  and  connected  to  bone  by  at  least  one 
extremity,  through  means  of  tendinous  or  fibrous  structure.  In 
fishes,  the  muscular  fibres  are  soft,  gelatinous,  and  colourless  as  in 
the  in  vertebrata,  and  the  embryos  of  the  higher  vertebrated  classes. 
In  the  salmon,  however,  they  are  of  a  higher  red,  especially  about 
the  head ;  and  in  the  lamprey  they  are  blackish  gray.  The 
arrangement  of  the  muscles  in  the  osseous  fishes  is  such,  that  a 
large  mass  extends  from  head  to  tail  on  each  side,  divided  by  fibrous 
bands  into  numerous  strata.  The  active  movements  of  fishes  are 
not  subject  to  much  variety ;  their  ascent  or  descent  is  effected 
by  the  compression  or  expansion  of  the  air-bladder,  and  by  their 
pectoral  fins,  whilst  they  are  impelled  forwards  by  the  lateral  motion 
of  the  tail  opposed  by  the  resistance  of  the  water.  When  the 
swimming  bladder  is  absent,  as  in  the  sole  genus,  or  very  small,  as 
in  the  cobitis  fossilis,  the  animal  either  remains  at  the  bottom,  or 
swims  on  one  side  by  the  vertical  motions  of  the  tail.  The  remora, 
lump-sucker,  and  others  are  provided  with  a  muscular  disk  in  the 
form  of  a  sucker,  by  which  they  adhere  to  other  fish  or  bodies 
moving  through  the  water:  so  powerful  is  the  muscular  tail  of  the 
salmon,  that,  aided  by  the  great  elasticity  of  its  spine,  it  is  able  to 
mount  over  cataracts  fifteen  feet  high.  The  shark  is  especially 
remarkable  for  speed,  so  much  so,  that  according  to  a  calculation  of 
Sir  E.  Home,  it  would,  if  not  compelled  to  rest,  swim  over  the  cir- 
cumference of  the  globe  in  thirty  weeks. 

AMPHIBIA. 

The  proteus,  siren,  and  the  tadpoles  of  the  higher  anurous  spe- 
cies, are  moved  through  the  water  by  the  same  kind  of  lateral 
motion  of  the  spine  and  tail  as  in  fishes.  The  oreat  lateral  mus- 
cles that  accomplish  these  motions  are  still  pale,  bloodless,  and 
feeble,  and  their  connecting  cellular  tissue  is  soft,  scanty,  and 
colourless;  the  muscles  are  slightly  connected  to  the  skin,  and  pre- 
sent but  little  appearance  of  tendinous  structure.  So  far  the  mus- 
cular system  closely  resembles  that  of  fishes,  but  in  the  adult  state 


MUSCULAR  SYSTEM  IN  THE  VERTEBRATA.  43 

of  the  anurous  species,  it  presents  characters  very  remote  from  them, 
arising  from  their  great  extent  of  respiration,  and  their  inhabiting  a 
rarer  medium.  The  oblique  caudal  muscles  in  the  tadpole  of  the 
tailless  tribe,  become  absorbed  with  the  vertebras  to  which  they  are 
attached,  as  the  animal  assumes  its  permanent  form ;  but  its  change 
of  habits  is  still  provided  for  by  the  great  development  of  the 
muscles  of  the  posterior  extremity,  in  fact  they  closely  resemble 
those  of  the  human  leg;  and  hence  the  act  of  swimming  in  man 
is  an  accurate  imitation  of  that  of  the  frog.  In  this  animal,  the 
extensors  are  much  stronger  than  the  flexors  of  the  leg,  and  those 
of  the  arm  are  but  feebly  developed. 


REPTILIA. 

The  rarity  of  the  medium  through  which  the  air-breathing  rep- 
tiles move,  at  once  declares  an  increased  development  of  muscular 
energy  in  this  class.  In  the  progressive  motion  of  serpents,  their 
vertebral  column  forms  several  S-shaped  lateral  curves;  is  shortened, 
and  again  stretched  forwards,  whilst  the  posterior  part  of  the  body 
is  fixed:  this  rapidly  performed  constitutes  a  leap  or  dart.  The  ribs 
being  free  at  their  distal  extremities,  admit  of  extensive  motion,  and 
are  furnished  with  large  intercostal  muscles  of  various  lengths, 
some  passing  from  rib  to  rib,  and  others  over  one  or  more  to  have 
distant  insertions.  These  muscles  have  small  shining  tendinous 
bands,  by  which  a  great  number  can  be  attached  to  a  small  space, 
and  thus  admit  of  great  variety  in  the  movements  of  the  ribs, 
which  are  not  only  subservient  to  respiration,  but  to  progressive 
motion  in  these  animals.  The  muscles  of  the  head  are  strong,  and 
in  the  rattle-snake  and  others,  a  portion  of  the  temporal  extends 
forwards  like  a  buccinator,  to  embrace  the  poison  gland  and  force 
its  secretion  into  the  perforated  fang. 

The  saurian  reptiles  possess  members  sometimes  organised  for 
progression  on  the  surface,  sometimes  for  climbing,  sometimes  for 
swimming,  and  occasionally  for  flying ;  hence  their  muscles  are 
more  numerous  and  complicated  than  in  serpents.  A  rudiment  of 
diaphragm  may  be  perceived  in  the  dragons  and  geckos  ;  and  in  the 
prehensile  tongue  of  the  chameleon  there  resides  a  beautiful  muscu- 
lar apparatus  ordained  to  govern  its  stealthy  movements  in  obtaining 
his  food,  and  as  Sir  C.  Bell  aptly  describes  it,  he  lies  more  still  than 
the  dead  leaf,  his  skin  is  like  the  bark  of  the  tree,  and  takes  the  hue 
of  surrounding  objects.  Whilst  other  animals  have  excitement 
conforming  to  their  rapid  motions,  the  shriveled  face  of  the  cha- 
meleon hardly  indicates  life ;  the  eyelids  are  scarcely  parted  ;  he 
protrudes  his  tongue  with  a  motion  so  imperceptible  towards  the 
insect,  that  it  is  touched  and  caught  more  certainly  than  by  the 
most  lively  action.  In  the  chelonia,  the  muscles  of  the  extremities 
together  with  those  of  the  shoulders  and  pelvis  are  well  marked, 
whilst  those  of  the  jaws,  lips,  and  chest  are  almost  wholly  absent. 


44  EVERS'S  COMPARATIVE  ANATOMY. 


AVES. 


A  greater  degree  of  uniformity  pervades  the  muscular  system  of 
this  than  any  other  of  the  vertehrated  classes,  yet  it  will  be  found  to 
present  many  peculiarities.  From  the  rarity  of  the  element  they 
inhabit,  as  well  as  from  their  rapid  and  long  continued  movements 
through  it,  their  muscles  require  a  considerable  degree  of  vital 
energy,  hence  they  are  red,  vascular,  dense,  and  irritable  in  the 
high  flying  and  rapacious  tribes,  although  pale,  soft,  and  feeble  in 
those  of  heavier  and  slower  habits.  The  fleshy  portions  of  the 
muscles  are  short  and  thick,  whilst  the  tendons  are  long,  slender, 
dense,  and  often  ossified ;  their  trunk  being  almost  fixed,  the 
muscles  of  the  dorsal  and  lumbar  regions  are  feeble  and  indistinct, 
those  of  the  neck,  on  the  contrary,  are  well  developed  in  accordance 
with  the  perfect  and  varied  motions  of  this  part  of  the  spine.  The 
muscles  of  the  abdomen  are  week  and  feeble,  and  the  diaphragm  so 
imperfect  in  the  centre  as  to  allow  the  heart  to  come  in  contact 
with  the  liver  as  in  reptiles.  Of  all  the  muscles,  none  reach  so 
great  a  degree  of  development  as  those  of  the  anterior  extremity, 
especially  those  attached  to  the  humerus.  Birds  possess  three  pec- 
toral muscles,  an  anterior,  middle,  and  posterior:  they  are  all 
attached  to  the  sternum  and  the  proximal  extremity  of  the  humerus. 
In  birds  of  flight,  the  great  pectoral  often  equals  in  weight  all  the 
other  muscles  of  the  body  combined.  The  latissimus  dorsi  and 
deltoid  are  feebly  developed,  whilst  the  psoEe,  obturator  externus, 
and  quadratus  lumborum,  are  wholly  absent.  The  muscles  of  the 
lower  extremity  are  remarkable  for  their  long,  slender  tendons,  and 
especially  for  the  beauty  and  perfection  of  the  mechanism  by  which 
they  support  the  bird  when  asleep  on  roost,  without  any  muscular 
action.  This  is  accomplished  by  the  gracilis,  which,  arising  from 
the  pubis,  descends  along  the  inner  side  of  the  thigh,  and  ends  in  a 
strong  tendon,  which  passes  in  front  of  the  knee-joint,  and  subse- 
quently over  the  projection  of  the  heel  to  terminate  by  attaching 
itself  to  the  outer  origin  of  the  flexor  digitorum  perforatus.  From 
this  disposition  it  results,  that  the  more  the  joints  are  bent,  the 
firmer  the  twig  on  which  the  bird  rests,  is  grasped,  and  the  heavier 
it  sleeps,  the  more  secure  it  is.  Every  one  is  familiar  with  the 
fact  of  birds  generally  sleeping  on  one  leg,  this  is  for  the  purpose 
of  throwing  the  entire  weight  of  their  body  on  it,  and  so  grasping 
the  firmer,  and  in  order  to  increase  the  effect  by  adding  to  the 
weight  of  the  body,  some  birds  are  in  the  habit  of  never  going  to 
roost  without  grasping  a  stone,  or  some  ponderous  body  in  the 
other  foot. 

Flight,  which  is  the  most  chracteristic  mode  of  progression  in 
birds,  is  effected  by  the  animal  springing  into  the  air ;  or,  where  the 
legs  are  so  short,  and  the  wings  so  Ions:  that  it  cannot  jump  high 
enough  to  gain  the  requisite  space  for  the  expansion  of  the  wing, 
it  throws  itself  from  some  elevated  point.     The  humerus  is  next 


MUSCULAR  SYSTEM  OF  THE  VERTEBRATA.  45 

raised,  and  the  fore-arm  extended,  a  considerable  extent  of  sur- 
face thereby  gained ;  the  entire  member  being  then  forcibly 
depressed,  the  resistance  which  it  receives  from  the  air,  effects  the 
elevation  of  the  bird;  velocity  of  flight  depends  upon  the  rapidity 
with  which  these  strokes  succeed  each  other.  The  eider-duck  is 
supposed  to  fly  90  miles  an  hour;  the  hawk  150,  and  everyone 
has  heard  of  the  falcon  belonging  to  Henry  IV.  king  of  France, 
flying  in  one  day  from  Fontainbleau  to  Malta,  a  distance  of  1350 
miles. 


MAMMALIA. 

Some  of  the  animals  composing  this  class  are  destined  to  move 
like  fishes  through  a  watery  element,  some  to  fly  through  the  air 
like  the  feathered  tribes,  some  to  climb  treess,  some  to  dig  and 
burrow  in  the  earth,  and  others  to  walk  upon  its  surface.  Habits 
so  diversified  bespeak  corresponding  diversities  of  muscular  arrange- 
ment. Many  approximations  to  the  human  type  present  themselves 
on  the  one  hand,  and  indisputable  recurrences  of  simpler  forms  on 
the  other.  The  fleshy  portions  of  the  muscles  are  generally  large 
and  plump,  proportioned  to  the  size  of  the  body,  or  the  massive 
bones  of  the  skeleton.  The  respiration  being  here  less  extensive, 
and  the  circulation  more  slow,  than  in  birds,  the  temperature  is 
lower,  the  muscular  fibre  less  dense,  and  the  tendons  less  prone  to 
undergo  ossific  changes. 

The  arrangement  of  the  muscles  in  the  cetacea  nearly  coincides 
with  that  in  fishes,  the  latter  moving  horizontally,  the  former  chiefly 
in  a  verticle  direction.  The  muscles  of  the  ribs,  spine,  pharynx, 
os  hyoides,  and  exterior  naresa  are  well  developed,  those  of  the  pelvis 
and  posterior  extremities  disappear  with  those  parts,  and  the  muscles 
of  the  anterior  extremities  are  curtailed  and  simplified,  least  so, 
however,  in  the  phytophagous  cetacea.  The  large  herbivorous 
quadrupeds  require  strong  muscles  to  move  their  massive  and 
heavy  trunks,  and  the  active  and  predatory  habits  of  the  carnivora 
demand  a  still  greater  development  of  this  system.  In  theruminan- 
tia,  pachydermata,  and  those  animals  without  clavicles,  the  anterior 
extremities  are  placed  under  the  trunk,  which  is  suspended  between 
their  long  vertical  scapulas  by  the  great  serrati  muscles,  in  many 
instances  prodigiously  developed.  The  buffalo,  the  bull,  and  others 
of  the  ruminants,  with  many  of  the  pachyderms,  have  the  muscles 
of  the  neck  large  and  powerful  to  move  their  heavy  heads,  which 
are  often  armed  with  large  teeth,  tusks,  a  proboscis,  or  huge  horns. 
The  external  muscles  of  the  ear  are  greatly  developed  in  many  of 
the  herbivorous  quadrupeds,  and  the  muscles  of  the  nose  in  the 
hog  tribe. 

The  panniculus  carnosus.  which  is  thin,  and  finely  spread  over 
the  trunks  of  the  pachydermata,  is  strong  and  fleshy  in  the  soft 
skinned  ruminantia,  where  it  is  attached  to  the  humerus  and  to  the 
femur.     In  the  mammalia  covered  with  spines,  as  the  echidnia,  the 


46 

hedge-hog,  and  the  porcupine,  and  those  covered  with  scales,  as  the 
rnanis  and  the  armadillo,  this  muscle  is  important  in  erecting  or 
moving  these  epidemic  organs,  and  in  coiling  or  uncoiling  the  body. 
In  the  mole,  and  those  animals  that  dig  the  earth,  the  flexors  of  the 
arm,  the  pectoralis  major,  the  latissimus  dorsi,  and  the  teres  major, 
are  of  vast  size.  In  the  rodentia,  the  muscles  are  pale,  and  those  of 
the  jaws  of  great  magnitude.  The  marsnpiata  have  the  panniculus 
carnosus  extended  over  the  pouch  in  such  a  manner  as  to  support 
the  young  abortive-like  fretus,  and  force  the  mammary  secretion 
into  its  mouth.  The  arrangement  of  the  muscles  approaches  nearer 
to  the  human  type  in  the  quadrumana  than  in  any  others  of  the 
mammalia.  In  them  the  flexor  muscles  are  strongly  developed  on 
all  their  extremities.  The  thumbs,  have  no  long  separate  flexors, 
but  receive  tendons  from  the  flexors  of  other  fingers.  r^ne  P^an~ 
taris  muscle,  which  is  very  fleshy  in  monkeys,  instead  of  termina- 
ting, as  it  does  in  man,  by  insertion  in  the  os  calcis,  passes  over  that 
bone  to  be  connected  with  the  planter  fascia  and  flexor  perforatum. 
In  other  quadrupeds  it  passes  over  the  os  calcis  to  the  sole  of  the 
foot,  and  supplies  the  place  of  the  flexor  digitorum  brevis.  The 
glutaeus  maximus,  which  is  the  largest  muscle  of  the  human  body, 
is  small  and  feeble  in  the  simise  and  other  animals,  its  chief  use  being 
to  support  the  trunk  upon  the  lower  extremity,  and  thus  assist  in 
maintaining  the  erect  attitude,  and  not,  as  the  pious  Spigelius 
imagined,  to  form  a  soft  cushion  for  the  body  to  rest  on  during 
divine  cogitation. 

Finally,  the  extensors  of  the  knee,  the  flexors  of  the  toes,  and  the 
other  muscles  forming  the  calf  of  the  leg.  are  relatively  larger  in  the 
human  subject  than  in  any  other  animal. 

RECAPITULATION. 

1.  Muscular  fibres  have  been  satisfactorily  shown  to  exist  in  the 
higher  species  of  the  radiata. 

2.  Muscle  is  found  all  through  the  articulate  and  molluscous 
classes,  but  better  and  more  uniformly  developed  in  the  former. 

3.  The  soft  parts  are  uniformly  placed  external  to  the  hard,  in 
the  vertebrated  classes. 

4.  The  muscles  in  fishes  are  generally  soft  and  pale,  as  in  the 
lower  classes. 

5.  In  the  amphibia,  the  muscles  present  different  characters  in 
the  tadpole  and  adult  state. 

6.  Great  variety  in  the  reptiles,  chiefly  referable  to  their  diversi- 
fied habits. 

7.  The  muscular  system  in  birds  is  characterised  by  great 
uniformity  throughout  the  class. 

8.  The  muscles  of  the  aquatic  mammalia  resemble  those  of 
fishes. 

9.  Serrati  magni  greatly  developed  in  the  quadrupeds  not  pos- 
sessing clavicles. 


NERVOUS  SYSTEM  IN  THE  INVERTEBRATA.  47 

10.  Panniculus  carnosus  best  marked  in  the  echidna,  the  hedge- 
hog, the  porcupine,  the  manis,  the  tatu,  the  marsupiata,  and  The 
thin-skinned  ruminants  ;  less  so  in  the  pachydermata,  and  absent 
from  some,  as  the  hog.  It  is  found  in  monkeys,  but  not  in  the 
chimpanse. 

11.  Lattismus  dorsi,  teres  major,  &c,  are  very  powerful  in  the 
mole  and  ant-eaters. 

12.  The  plantaris,  which  is  rudimental  in  man,  is  large  in  mon- 
keys and  some  quadrupeds. 

13.  Man  is  characterised  by  the  magnitude  of  his  buttocks,  thio-hs, 
and  calves. 


CHAPTER  VII. 

ON  THE  NERVOUS  SYSTEM  IN  THE   INVERTEBRATA. 

This  system,  when  perfectly  developed,  consists  of  an  internal  or 
central,  and  an  external  or  circumferential  portion  ;  to  the  latter 
belong  the  nerves  and  ganglions  ;  to  the  former,  the  spinal  cord,  the 
medulla  oblongata,  the  cerebellum,  and  the  cerebrum.  The  nervous 
system  presides  over  the  movements  of  our  muscles  and  the  sensi- 
bility of  our  bodies;  by  it  we  are  connected  with  surrounding 
objects,  and  an  injury  inflicted  on  any  part  of  the  body,  at  once 
declares  the  extent  of  its  distribution,  as  well  as  the  close  relation 
that  subsists  between  its  several  parts. 

The  nervous  system  has  been  detected  in  every  division,  although 
not  in  every  class,  of  the  animal  kingdom  :  it  commences  its  develop- 
ment at  the  circumference,  and  grows  towards  the  centre,  and  its 
forms  corresponds  pretty  closely  with  that  of  the  body  of  the  animal. 

The  nervous  matter  is  extremely  soft  in  the  inferior  grades  of 
animals,  as  well  as  in  the  embryo  of  the  higher  classes  ;  and  its 
colour  presents  some  variety,  being  bright  red  in  the  helix  stagnalis  • 
blackish  red  in  the  aplysias ;  and  bright  yellow  in  the  common  fresh 
water  muscle.  The  nerves  are  composed  of  tubes  filled  with  minute 
globules.  The  brain  is  also  composed  of  globules,  eight  times 
smaller  than  those  of  the  blood,  larger  and  more  numerous  in  the 
medullary,  than  in  the  cineritious  substance,  and  in  the  former  dis- 
posed in  lines  which  gave  it  its  fibrous  character. 

Cyclo-neura,  Grant. — In  the  two  first  classes  of  this  division, 
the  polygastrica  and  the  porifera,  no  nervous  filaments  have  been 
detected,  yet,  from  their  active  movements,  their  sensibility  to  the 
impression  of  light,  and  their  consciousness  of  each  others  approach, 
it  is  but  reasonable  to  infer  the  existence  of  a  nervous  system  in 
them,  though  from  its  transparency  or  some  other  cause,  it  cannot 
be  demonstrated.  Both  nerves  and  ganglions  are  found  to  exist  in 
the  three  remaining  classes  of  the  radiata.  Distinct  nervous  fila- 
ments surround   the   muscular  foot   of  the   actinia;  and   in  the 


48  EVERS'S  COMPARATIVE  ANATOMY. 

acaiephae  and  echinodermata,  fine  nervous   filaments  and   small 
white,  ganglions  surround  the  entrance  of  the  alimentary  canal. 

Dlplo-neura,  Grant.— In  this  great  division,  the  nervous 
system,  presents  the  same  extended  form  as  the  body,  placed  on  the 
ventral  surface  of  the  alimentary  canal,  and  except  in  the  higher 
classes,  not  enclosed  in  an  osseous  sheath.  Among  the  higher 
forms  of  the  entozoa,  as  the  ascaris,  two  fine  nervous  filaments 
extend  along  the  median  line  of  the  abdomen,  separating  to  embrace 
the  oesophagus,  and  the  vulva  of  the  female.  In  the  notommata 
clavulata  of  the  rotifera,  we  find  nine  pairs  of  ganglions  disposed 
along  the  course  of  the  lateral  columns.  Scarcely  a  trace  of  ner- 
vous system  can  be  perceived  in  the  simple  forms  of  the  annelida. 
In  the  nereids,  however,  and  many  others  of  this  class,  the  sympa- 
thetics  become  quite  distinct ;  and  numerous  nerves  are  seen  to  pass 
off  in  the  lateral  direction.  The  common  leech,  which  presents 
about  eighty  rings  in  the  trunk  of  its  body,  has  five  and  twenty 
ganglia  placed  along:  the  abdomen,  approximated  at  the  two  extre- 
mities of  the  column.  In  the  most  inferior  of  the  diversified  class 
of  the  crustaceans,  the  nervous  system  presents  itself  in  the  form  of 
two  slender  abdominal  filaments,  in  imitation  of  what  we  have  seen 
in  the  preceding  classes,  and  by  a  gradual  development  from  the 
peripheral  to  the  central  parts,  it  arrives  at  that  concentration  of 
nervous  ganglia  around  the  oesophagus,  which  connects  the  highest 
of  the  articulate  with  the  molluscous  classes. 

'  Cyclo-gangliata.— The  greater  number  of  the  mollsuca  being 
aquatic,  their  nerves  present  the  same  pale  and  soft  characters 
observed  in  the  other  aquatic  invertebrates  ;  hence  the  difficulty  of 
indicating  their  particular  distributions.  Here  as  in  the  radiata,  the 
same  tendency  to  accumulate  nerves  around  the  entrance  to  the 
alimentary  canal  prevails,  but  in  this  case  more  generally  accom- 
panied with  ganglia.  In  the  lowest  classes  of  the  division,  as  the 
tunicata  and  conchifera,  the  nervous  chords  are  placed  beneath  the 
alimentary  canal  ;  in  the  two  next  classes  gasteropoda  and  ptero- 
poda,  they  are  more  in  the  vicinity  of  the  stomach ;  arid  in  the  ce- 
phalopoda, which  is  the  last  and  highest  of  the  division,  the  nervous 
ganglia  attain  a  more  elevated  position,  they  cease  to  embrace  the 
oesophagus;  and  a  distinct  brain,  as  in  the  vertebrata,  with  nume- 
rous symmetrical  ganglia  along  the  abdomen  take,  their  place. 


CHAPTER  VIII. 

NERVOUS  SYSTEM  IN  THE  VERTEBRATA. 

PISCES.  ^ 

We  no  longer  find  the  nervous  system  perforated  by  the  alimen- 
tary  tract.     On,   the   contrary,   in   all    the  succeeding  classes,    it 


NERVOUS  SYSTEM  IN  THE  VERTEBRATA.  49 

occupies  a  dorsal  situation,  and  is  protected  by  an  osseous  sheath. 
In  the  lowest  orders  of  fishes,  as  the  lamprey,  and  the  gastrobranchus, 
we  perceive  a  repetition  of  the  two  nervous  columns  extending 
along  the  back  as  observed  in  the  worm.  This  simple  condition 
resembles  the  embryo  state  of  this  system  in  the  highest  grades  of 
the  vertebrata,  previous  to  the  development  of  their  extremities. 
With  kw  exceptions  the  spinal  chord  extends  the  whole  length  of 
the  vertebral  column  ;  whence,  from  the  great  number  of  vertebrae, 
it  attains  a  very  remarkable  length.  In  some,  however,  as  the 
lophius  piscatorius,  it  is  stated  to  be  very  short,  forming  a  kind  of 
Cauda  equina  as  in  man.  It  usually  terminates  in  a  single  thread, 
presenting  several  enlargements  throughout  its  tract,  which  corres- 
pond very  accurately  with  the  number,  magnitude,  and  situation  of 
the  extremities.  For  instance,  when  the  anterior  members  are  very 
large,  as  in  rays  and  flying-fishes,  the  anterior  enlargements  are 
proportionally  developed  ;  and  where  a  large  caudal  fin  is  to  be 
supplied,  the  chord  presents  a  sensible  enlargement  posteriorly 
where  the  nerves  join  it.  The  spinal  marrow,  here,  as  in  the 
human  foetus,  usually  contains  a  canal  of  considerable  size,  and  is 
distinguished  by  an  anterior,  a  posterior,  and  two  lateral  grooves. 
From  the  latter,  the  nerves  arise  by  two  roots,  the  posterior  or  sen- 
sitive root  having  a  ganglion  on  it,  receives  the  anterior  root  im- 
mediately external  to  the  canal. 

The  brain  m  fishes  does  not  fill  the  cavity  of  the  cranium,  a 
considerable  portion  of  it  being  occupied  by  the  soft  cellular  tissue 
of  the  arachnoid.  The  medulla  oblongata  is  of  great  length,  lobed, 
and  deeply  grooved  above  by  the  calamus  scriptorius. 

Tn  most  fishes,  the  optic  lobes  are  larger  than  the  hemispheres, 
they  are  hollow  and  communicate  freely  with  each  other  and  with 
the  fourth  ventricle.  The  earlier  they  are  examined  the  larger  they 
are  found  to  be  ;  their  development  is  proportionate  to  that  of  the 
optic  nerves  and  eyes,  and  inversely  to  that  of  the  cerebrum  and 
cerebellum.  The  cerebral  hemispheres  are  small  in  the  osseous, 
apodal,  and  cyclostome  fishes,  and  in  the  plagiostome  species  they  are 
larger  than  the  optic  tubercles.  In  the  osseous  fishes  they  resemble 
the  embryo  condition  of  the  human  brain  in  being  destitute  of  ven- 
tricles, and  having  no  convolutions  on  the  surface.  In  sharks  and 
rays  the  hemispheres  attain  a  large  size,  present  irregularities  on 
the  surface,  and  ventricles  in  their  interior.  In  front  of  the  hemi- 
spheres are  placed  the  olfactory  tubercles,  elongated  transversely,  and 
exceeding  in  magnitude  the  hemispheres  themselves;  subject,  how- 
ever, to  considerable  variations,  regarding  form,  size,  and  situation. 

The  cerebellum  is  scarcely  to  be  recognised  in  many  of  the 
cyclostome  fishes.  When  present  it  appears  as  a  transverse  band, 
rising  vertically  in  the  osseous  fishes,  and  forming  a  small  vermiform 
median  lobe,  slightly  laminated  in  the  plagiostome  fishes.  In  sharks 
and  rays  not  only  does  this  median  lobe  attain  considerable  magni- 
tude, but  small  hemispheres  are  developed  laterally,  corresponding 
in  size  to  that  of  the  carpora  restiformia.  The  pineal  gland  is  found 
8 — e  evers  4 


50 

in  all  fishes,  lodged  between  the  hemispheres  and  optic  tubercles, 
but  so  small  in  the  osseous  tribes  that  its  existence  has  been  ques- 
tioned. These  several  lobes  are  covered  with  a  layer  of  cineritious 
substance,  and  closely  invested  by  a  delicate  layer  of  pia  mater; 
outside  of  which  is  the  soft,  gelatinous,  cellular  arachnoid  tunic,  and 
all  are  surrounded  by  an  envelope  of  dura  mater. 

Nerves. — The  olfactory  nerves  are  white  and  fibrous  ;  they  are 
very  large  in  the  rays  and  sharks,  and  in  many  instances  form  a 
ganglion  before  their  termination  ;  as  may  be  seen  in  the  carp. 
The  optic  nerves  are  developed  in  proportion  to  the  size  of  the  optic 
tubercles  and  eyes ;  hence  they  are  large  in  the  carp,  and  slender  in 
the  eel.  In  the  osseous  fishes  they  generally  cross  without  any  in- 
termingling of  fibres;  in  the  plagiostome  fishes  their  fibres  are 
blended  at  the  commissure  as  in  the  mammalia;  and  in  the  skate, 
the  right  nerve  goes  through  a  fissure  in  the  left.  The  third,  fourth, 
and  sixth  nerves  are  developed  in  proportion  to  the  size  of  the 
muscles  they  supply.  The  fifth  nerve  presents  a  greater  size,  and 
gives  off  more  branches  in  this  class  than  in  any  other  of  the  verte- 
brata.  The  ophthalmic,  superior,  and  inferior  maxillary  are  dis- 
tributed to  the  face,  palate  and  lower  jaw.  In  the  rays,  and  many- 
other  fishes,  it  sends  a  branch  to  the  ear,  and  in  the  torpedo,  to  the 
electrical  organs.  These  latter  are  composed  of  a  series  of  mem- 
branous cells  occupied  by  a  gelatino-albuminous  substance,  per- 
forming the  office  of  a  Leyden  jar  or  electrical  battery.  They  lie 
in  the  torpedo  on  the  upper  surface  of  the  lateral  fin.  In  the  elec- 
tric eel,  on  the  posterior  part  of  the  abdomen  ;  and  in  the  silurus 
electricus  they  are  situate  between  the  muscles  and  skin  over  the 
entire  body.  In  the  last  named  fish  the  nerves  appear  to  be  derived 
from  the  pneumo  gastric.  Both  portions  of  the  seventh  pair  are 
small  and  distributed  without  any  peculiarity.  The  pneumo-gas- 
tric  arises  from  the  side  of  the  medulla  oblongata,  behind  the  fifth 
pair ;  it  forms  a  large  ganglion  below  its  origin,  from  which 
branches  proceed  to  the  branchiae,  the  oesophagus,  the  stomach,  and 
rudimentary  lungs.  This  nerve  gives  off  also  a  branch  to  the 
tongue  analogous  to  the  glossopharyngeal,  and  one  to  the  lateral 
part  of  the  body  analogous  to  the  spinal  accessary,  both  of  which 
are  rudimental  in  fish.  The  ninth  pair  is  wholly  absent  and  its 
place  supplied  by  a  branch  from  the  fifth.  The  distribution  of  the 
spinal  nerves  is  very  simple,  and  their  development  is  always  pro- 
portioned to  the  size  of  the  fins  ;  the  sympathetic  is  very  slender, 
and  its  ganglions  small  in  fishes.  It  is  most  developed  in  the  pla- 
giostome chondropterygii,  and  least  so  in  the  cyclostome  species  ;  it 
receives  filaments  from  the  spinal  nerves,  and  its  meshes  accompany 
the  arterial  trunks  in  their  distribution  on  the  digestive,  respiratory, 
and  generative  organs. 

AMPHIBIA. 

The  condition  of  the  brain,  the  medulla  oblongata,  and  the  spinal 
chord  are  nearly  the  same  in  the  perennibranchiate  amphibia,  and 


NERVOUS  SYSTEM  IN  THE  VERTEBRATA.  51 

in  the  larva  state  of  those  which  undergo  metamorphosis,  as  are 
observed  in  the  osseous  fishes.  The  lobed  form  of  the  medulla 
oblongata,  the  small  cerebellum,  the  optic  thalami,  with  the  ventri- 
cles, and  the  diminutive  extent  of  the  hemispheres,  all  evince  a 
degree  of  perfection  not  much  above  that  noticed  in  fishes.  The 
spinal  chord  is  prolonged,  small  and  tapering  into  numerous  coc- 
cygeal vertebrae,  and  without  sensible  enlargements  where  the 
nerves  are  to  come  off  to  supply  the  future  members.  The  meta- 
morphosis of  the  caducibranchiate  species,  from  the  pisciform  to 
the  reptile  state,  develope  an  interesting  series  of  phenomena.  The 
hemispheres  become  enlarged,  the  cerebellum,  which  was  scarcely 
visible,  increases  in  size  across  the  median  line ;  as  the  limbs  begin 
to  appear,  the  spinal  marow  exhibits  corresponding  developments, 
but  dwindles  posteriorly  as  the  coccygeal  vertebrae  disappear.  So 
rapid  are  these  changes  in  the  nervous  system  of  the  frog,  that  we 
can  appreciate  them  from  day  to  day.  The  sympathetic  system  is 
more  distinct  in  this  class  than  in  that  of  fishes. 

REPTILIA. 

In  this  class  the  cerebral  hemispheres  exceed  in  size  the  optic 
lobes,  and  contain  a  distinct  ventricle.  The  cerebellum  is  remark- 
ably small  ;  and,  in  the  sauria  and  chelonia,  the  spinal  marrow 
presents  an  obvious  enlargement,  opposite  the  attachment  of  each 
nerve.  The  medulla  oblongata  is  broad  ;  the  nerves  are  large, 
compared  with  the  cerebral  centres,  but  present  no  peculiarity  of 
distribution.  The  plexuses  of  the  sympathetic  are  here  more 
closely  connected  with  the  arterial  trunks,  than  in  the  preceding 
classes. 

AVES. 

The  brain  and  spinal  chord  are  in  this  class  developed  with  more 
uniformity  and  perfection  than  in  the  cold-blooded  reptilia  ;  and 
bear  a  remarkable  correspondence  with  the  perfection  of  muscular 
energy  which  they  possess.  In  a  pigeon  weighing  3360  grains, 
without  the  feathers,  the  brain  weighed  37,  and  the  spinal  chord  11 
grains=48. 

The  spinal  chord  extends  from  the  foramen  magnum  to  the 
coccygeal  vertebrae,  where  it  is  greatly  reduced  in  size,  and  expends 
itself  in  distributing  a  few  nerves  through  the  lateral  foramina.  The 
length  of  the  chord  is  considerable,  compared  with  the  size  of  the 
brain  ;  its  shape  is  cylindrical ;  its  anterior  and  posterior  grooves 
are  very  distinct,  as  well  as  a  minute  canal  extending  through  its 
whole  length,  arising  from  the  union  of  the  two  halves  of  the 
chord:  the  dilatation  of  this  canal  in  the  pelvic  region,  is  called 
"rhomboidal  sinus."  The  spinal  chord  is  chiefly  composed  of 
white  matter,  but  contains  a  small  quantity  of  gray,  internally. 
Two  enlargements  occur  on  the  chord,  bearing  a  relative  size  to 
the  development  and  powers  of  the  extremities:  in  general  the 
posterior  enlargement  is  the  greater,  especially  when  the  business 


52 

of  progression  devolves  on  the  posterior  members,  as  in  strnthious 
birds.  The  form  of  the  chord  is  not  altered  in  the  alar  enlarge- 
ment, but  simply  increased  by  an  accession  of  gray  and  white 
substances; — the  lower  one,  on  the  contrary,  not  only  receives 
additional  matter,  but  the  pillars  separate,  so  that  the  fluid  in  the 
sinus  is  merely  covered  by  pia  mater. 

The  brain  of  the  bird  differs  from  that  of  the  reptile  in  the 
greater  size  of  the  cerebrum,  and  the  more  complex  structure  of 
the  cerebellum;  it  differs  from  the  brain  of  a  mammal  in  the 
smaller  size  of  the  cerebellum,  and  the  rudimentary  state  of  the 
fornix;  and  it  differs  from  the  brain  of  every  other  vertebrate  class 
in  the  inferior  position  of  the  optic  lobes.  The  cerebral  hemispheres 
are  generally  of  a  convex  condiform  shape,  with  the  apex  directed 
forwards;  they  are  disunited  through  their  whole  extent,  being 
only  joined  by  a  round  anterior  commissure;  they  are  destitute  of 
convolutions,  and  have  a  small  ventricle  in  their  interior.  The 
olfactory  tubercles  are  greatly  reduced  in  size,  and  retain  their 
tubular  communication  with  the  cerebral  ventricles.  The  optic 
lobes  are  small  ;  gray  on  the  surface,  white  internally,  and  contain 
each  a  small  ventricle  ;  they  are  connected  by  transverse  medul- 
lary bands  on  which  the  pineal  gland  rests,  with  its  peduncles 
directed  forwards  over  the  optic  thalami.  These  last  bodies  are 
covered  by  the  cerebral  hemispheres,  united  by  a  commissura 
mollis,  and  destitute  of  transverse  sulci.  The  medulla  oblongata 
is  large  and  wide;  its  components  are  marked  on  the  surface,  but 
it  is  without  tuber  annulare.  The  cerebellum  presents  a  median 
vermiform  lobe,  and  rudimentary  hemispheres,  sulcated  trans- 
versely, with  a  faintly-marked  arbor  vitae  in  the  interior.  The 
membranes  investing  the  brain  differ  but  little  from  those  of  the 
mammalia. 

Nerves. — The  nerves  in  this  class  present  but  few  striking  pecu- 
liarities, being  distributed  nearly  as  they  are  in  man.  The  olfactory 
arise  from  the  front  of  the  hemispheres,  pass  forwards  through 
distinct  osseous  canals  in  the  cribriform  plate,  and  are  distributed 
in  a  radiated  manner  on  the  superior  spongy  bone.  The  large 
optic  nerves  arise  from  the  optic  tubercles,  and  form  a  perfect 
decussation  in  front  of  the  infundibulum  ;  where,  as  in  the  iguana, 
an  incision  displays  a  mutual  intermixture  of  the  fibres.  The 
remaining  cerebral  nerves  are  distributed  pretty  nearly  as  in  mam- 
malia;  the  portio  dura  is,  however,  small  in  accordance  with  the 
insensibility  of  the  superficial  parts  of  the  face.  The  spinal  nerves 
correspond  in  number  to  the  vertebrae  ;  they  arise  by  two  roots,  the 
posterior  having  a  large  ganglion  on  it.  The  sympathetic,  which 
is  well  developed,  communicates  through  the  anterior  lacerated 
opening  with  the  fifth  and  sixth  nerves.  From  the  third  cervical 
vertebra  to  the  thorax,  it  is  contained  in  the  canal  in  the  transverse 
processes,  in  company  with  the  vertebral  artery.  It  form  a  series 
of  ganglions,  from  the  base  of  the  skull  to  the  end  of  the  coccyx ; 
and  communicates,  in  its  course,  with  every  neighbouring  nerve. 


NERVOUS  SYSTEM  IN  THE  VERTEBRATA.  53 


MAMMALIA. 

In  this  class  the  increased  development  of  the  nervous  system  is 
marked  by  the  size  and  length  of  the  spinal  chord ;  the  magnitude 
of  the  cerebrum  and  cerebellum,  and  the  number  of  their  gray 
deposits  and  commissures,  as  well  as  by  the  number  and  arrange- 
ment of  the  ganglions,  together  with  the  extent  and  systematic  dis- 
tribution of  the  great  sympathetic. 

The  spinal  chord  is  larger  in  proportion  to  the  size  of  the  body, 
but  smaller  when  compared  with  the  brain,  in  this  than  in  any  of 
the  preceding  classes;  its  internal  canal  has  almost  ceased  to  exist, 
and  its  lateral  portions  are  more  intimately  united.  It  is  shortest 
in  man,  quadrumana,  and  the  tailless  cheiroptera,  and  longest  in 
the  cetacea,  where,  as  in  apodal  fishes,  tadpoles,  serpents,  and  the 
human  embryo,  it  presents  no  posterior  enlargements.  In  the  long- 
tailed  quadrupeds  it  extends  to  the  sacrum;  the  posterior  groove  is 
generally  shallow,  though  sometimes  of  considerable  depth,  as  in 
cheiroptera  and  rodentia.  The  medulla  oblongata  is  small :  the 
corpora  pyramidalia  decussate  very  distinctly:  the  olivary  bodies 
are  small,  and  generally  contain  a  corpus  dentatum  in  their  interior, 
and  the  transverse  fibres  of  the  pons  or  great  cerebellic  commissure 
are  well  seen. 

Brain. — In  the  class  mammalia,  the  cineritious  matter  bears  a 
small  proportion  to  the  white  substance.  The  convolutions  are 
very  superficial  in  the  cetacea,  edentata,  ruminantia,  and  pachyder- 
mata,  and  wholly  absent  in  the  rodentia,  and  monotremata,  as  in 
birds;  whilst  they  are  deep  in  man,  monkeys,  and  carnivorous  ani- 
mals. The  optic  lobes,  without  cavities,  are  smallest  in  man, 
quadrumana,  and  carnivora,  larger  in  the  herbivora,  and  largest  of 
all  in  rodentia  and  edentata.  A  contrary  ratio  obtains  respecting 
the  development  of  the  cerebral  hemispheres,  and  the  olfactory 
tubercles.  The  anterior  and  inferior  cornua  of  the  lateral  ventri- 
cles, as  well  as  the  several  commissures,  are  always  present  in  this 
class.  The  posterior  lobe  of  the  brain,  and  the  posterior  cornua  of 
the  lateral  ventricle,  first  appear  in  the  quadrumana ;  the  former 
has  no  convolutions. 

The  vast  superiority  of  man  over  all  other  animals  in  mental 
faculties,  led  physiologists  at  a  very  early  period  to  seek  for  corres- 
ponding differences  in  the  brains  of  man  and  animals.  They 
compared  the  weight  of  the  brain  with  that  of  the  body,  and  their 
researches  led  them  to  conclude  that  man  had  the  largest  brain  in 
proportion  to  his  body.  Since  the  time  of  Aristotle  till  within  a 
late  period  this  opinion  has  been  received  :  but  more  modern  inves- 
tigations have  proved  that  the  proportion  of  the  brain  to  the  body 
in  some  birds  exceeds  that  of  man,  and  that  several  of  the  quadru- 
mana and  some  rodentia  equal  him  in  this  respect.  The  illustrious 
Soemmering  proposed  another  mode  of  comparison,  that  of  the 
ratio  which  the  mass  of  the  brain  bears  to  that  of  the  nerves  arising 
from  it,  and  in  this  point  of  view  man  is  decidedly  pre-eminent. 


54 

The  brain  of  man  far  exceeds  in  size  that  of  the  simiaa  compared 
with  the  nerves  proceeding  from  it,  and  in  these  latter  and  in  the 
seal  it  is  larger  in  proportion  than  in  other  animals,  while  it  is 
smallest  in  the  glires,  marsnpialia,  cheiroptera,  and  edentata.  The 
largest  brain  which  Soemmering  has  found  in  a  horse  weighed 
1  lb.  4oz.,  and  in  an  adult  man  was  2  lb.  5£oz. :  yet  the  nerves  arising 
from  the  former  were  ten  times  larger  than  those  of  the  latter. 
Coeteris  paribus^  small  animals  have  a  larger  brain  in  proportion 
to  their  size,  than  large  ones,  and  in  cold-blooded  animals  its  di- 
mensions are  very  small,  compared  with  those  of  a  higher  tempe- 
rature. The  following  table  shows  the  relative  weight  of  the  brain 
to  that  of  the  body  in  several  of  the  vertebrate  classes  of  animals: — 

Fishes. — Silurus  glanis,  one-1 887th  ;  dog-fish,  one-1344th  ;  shark, 
one-2496th  ;  carp,  one-560th. 

Reptiles. — Turtle,  one-5688th;  colubar  natrix,  one-792d ;  frog, 
(amphibious,)  one-172d. 

Birds. — Goose,  one-360th ;  duck,  one-257th  ;  eagle  one-260th  ; 
falcon,  one-102d  ;  sparrow,  one-25th  ;  canary-bird,  one-14th. 

Cetacea. — Porpoise,  one-93d;  dolphin,  one-102d,  one-60th,  one- 
36th,  one-25th. 

Solipeda. — Ass,  one-254th  ;  horse,  one-700th;  one-400th. 

Ruminantia. — Ox,  one-S60th;  stag,  one-290th;  sheep,  one-192d; 
calf,  one-2l9tb. 

Pachydermata. — Wild  boar,  one-672d ;  domestic,  one-512th  ; 
elephant,  one-500th. 

Rodentia. — Beaver,  one-290th ;  hare,  one-228th ;  rabbit,  one- 
152d;  rat,  one-76th;  mouse,  one-43d;  field-mouse,  one-3 1st. 

Carnivora. — Dog,  one-305th,  one-47th  ;  fox,  one-205th  ;  wolf, 
one-230th;  cat,  one-156th,  one-82d ;  ferret,  one-138th. 

Plantigrada. — Hedge-hog,  one- 1 68th;  bear,  one-265th;  mole, 
one-36th. 

Cheiroptera. — Bat,  one-96th. 

Le?nurs. — Vari,  one-84th;  mococo,  one-61st. 

Baboons. — Magot,  one  105th;  great  baboon,  one-104th  ;  macaque, 
one-85th. 

Apes. — Mangabey,  one-48th;  the  monk  ape.  one-44lh  ;  malbrouk, 
one-24th. 

Sapajous. — (American  apes)  Coa'ita,  one-41st;  Sai,  one-25th ; 
Saimiri,  one-22d. 

Onranfr-outangs. — The  gibbon,  one-48th;  chimpanse,  26  inches 
in  height,  11  oz.  7dr. 

Child  of  six  years,  one-22d;  adult  man,  one-35th. 

The  Cerebellum  is  smaller  in  proportion  to  the  cerebrum  in 
man,  the  saimiri,  and  the  ox,  than  in  any  others  of  the  mammalia. 
In  the  human  subject  and  in  ourangs  only,  is  it  covered  by  the 
posterior  lobes  of  the  brain.  The  superior  vermiform  process  and 
the  hemispheres  of  the  cerebellum  are  developed  in  every  class 
in  the  inverse  ratio  of  each  other.  In  the  saimiri  ape,  the  cerebel- 
lum is  to  the  cerebrum  as  1  to  14 ;  in  man  and  the  ox,  1  to  9 ;  in 


NERVOUS  SYSTEM  IN  THE  VERTEBRATA.  55 

the  monk  ape  and  the  dog,  1  to  8 ;  in  the  magot,  papio,  and  wild 
boar,  1  to  7 ;  in  the  sai  and  hare,  1  to  6 ;  in  the  mole,  1  to  4 ;  in 
the  rat  and  beaver,  1  to  3 ;  and  in  the  mouse,  1  to  2. 

Nerves. — The  olfactory  nerves  are  largest  in  the  ruminantia, 
pachydermata,  and  carnivora,  smaller  in  the  cheiroptera  and  qua- 
drumana,  and  discoverable  with  difficulty  in  many  of  the  cetacea. 
In  the  squirrel,  rabbit,  hare,  and  other  large-eyed  nocturnal  quadru- 
peds, the  optic  nerves  are  very  large;  they  are  small  in  rats,  mice, 
bats,  hedge-hogs,  and  subterranean  moles,  and  in  the  sorex  arraneus, 
mus  typhlus,  muscapensis.  and  others,  they  are  said  to  be  altogether 
wanting.  They  unite  before  the  infundibulum,  and  form  a  partial 
decussation  of  their  fibres.  The  third,  fourth,  and  sixth  nerves  are 
distributed  as  in  man,  and  are  very  small  in  subterranean  animals. 
Of  all  the  cerebral  nerves,  none  reaches  so  great  a  degree  of  deve- 
lopment as  the  fifth  pair,  in  the  inferior  classes  of  animals  and  in 
the  foetal  state  of  the  human  subject:  it  is  also  of  enormous  size  in 
most  aquatic  birds.  Its  branches  are  freely  and  extensively  distri- 
buted in  those  animals  with  proboscis,  long  muzzles,  large  lips,  and 
broad  bills,  as  the  cetacea,  ruminantia.  pachydermata,  carnivora, 
and  ornithorhynchi,  and  also  in  those  possessing  horns,  spines, 
bristles,  and  whiskers.  This  nerve  is  supposed  to  preside  over  the 
peculiar  instinctive  actions  so  remarkable  in  those  grades  of  ani- 
mals which  indicate  an  inferior  degree  of  mental  endowment,  and 
this  opinion  receives  strength  from  the  fact  of  its  great  size  in  the 
very  early  periods  of  human  existence,  when  we  know  the  actions 
are  purely  instinctive.  The  remaining  cerebral,  the  spinal,  and  the 
sympathetic  nerves  are  distributed  so  much  after  the  human  type 
as  to  merit  no  particular  remarks. 

In  most  mammalia  the  arteries  of  the  brain  form  a  complicated 
net-work  around  the  petuitary  body  at  the  base  of  the  cranium 
named  rete  mirabile,  obviously  designed  to  impede  the  flow  of 
blood  to  the  brain,  in  those  animals  with  pendent  heads.  The 
veins  occasionally  run  in  osseous  canals  in  order  to  avoid  pressure; 
this  is  well  seen  in  the  cribriform  plate  of  the  mole's  skull,  and  in 
the  bony  falx  cerebri  of  the  porpoise.  A  bony  falx  cerebri  is  also 
found  in  the  ornithorhynehus,  an  animal  which  abounds  in  in- 
stances of  anomalous  structure.  Animals  which  possess  a  bony 
tentorium  are  of  far  more  common  occurrence:  it  is  well  developed 
in  most  species  of  the  cat  and  bear  kind;  it  is  not  so  well  marked 
in  the  dog,  seal,  horse,  and  wombat,  and  it  is  merely  rudimentary 
in  the  pig,  the  rabbit,  and  the  mouse. 

It  has  been  generally  supposed  that  these  structures  exist  in  such 
animals  only  as  jump  far,  and  that  they  served  the  purpose  of  pro- 
tecting the  respective  portions  of  the  cerebrum  and  cerebellum  from 
undue  pressure  during  these  active  movements,  but  this  opinion  is 
rendered  quite  untenable  from  the  fact  of  their  absence  in  many 
animals  notable  for  jumping,  as  the  wild  goat,  (fee,  and  their  pre- 
sence in  those  animals  alike  remarkable  for  their  slow  and  easy 
movements,  as  the  bear.     It  is  more  probable  they  exist  for  the 


56  EVERS's  COMPARATIVE  ANATOMY. 

purpose  of  obviating  the  concussion  which  would  arise  from  the 
strong  exertions  in  biting;  for  such  exertions  are  made  by  all  the 
animals  which  possess  them,  even  by  the  horse  in  his  wild  state. 

RECAPITULATION. 

1.  A  nervous  system  exists  in  every  class  of  animals,  though  not 
in  all  the  animals  of  each  class. 

2.  In  the  invertebrate  classes  it  has  a  peculiar  tendency  to  accu- 
mulate around  the  oesophagus. 

3.  In  all  the  vertebrata  its  principal  parts  are  protected  by  osseous 
sheaths. 

4.  The  spinal  marrow  is  tubular  in  the  human  embryo,  and  most 
of  the  lower  vertebrata. 

5.  This  system  undergoes  remarkable  changes  in  the  amphibia, 
during  their  metamorphosis. 

6.  It  is  highly  developed,  and  with  great  uniformity  in  birds. 

7.  The  chord  presents  enlargements  corresponding  in  size  to  the 
members  most  used. 

8.  The  spinal  chord  bears  a  large  ratio  to  the  size  of  the  body  in 
most  mammalia. 

9.  Man's  superiority  is  due  to  his  mental  faculties. 

10.  The  brain  is  larger  in  proportion  to  the  size  of  the  nerves 
connected  with  it  in  man  than  in  any  other  animal. 

11.  The  fifth  cerebral,  or  the  nerve  of  instinct,  is  very  large  in 
most  mammalia,  and  in  the  foetal  state  of  the  human  subject. 


CHAPTER  IX. 

ORGANS  OF  SENSE. 

General  observations. — The  organs  of  sense  are  those  instru- 
ments which  are  placed  upon  the  distal  extremities  of  certain  cere- 
brospinal sensitive  nerves,  whose  office  being  to  establish  a  relation 
between  the  internal  sentient  principle  and  the  external  objects  of 
surrounding  nature,  are  necessarily  placed  in  connection  with  the 
external  surface  of  animals,  and  generally  in  the  neighbourhood  of 
the  entrance  of  the  alimentary  canal.  They  are  more  numerous, 
more  varied,  and  more  perfect  in  the  higher  than  in  the  lower  tribes 
of  animals,  but  they  are  more  developed  in  the  active  insects  and 
others  of  the  articulata,  than  in  the  slow  and  torpid  mollusca,  and 
they  attain  their  greatest  degree  of  perfection  in  the  vertebrata  where 
the  most  complicated  and  delicate  forms  of  organisation  are  con- 
signed to  their  careful  watch. 

Vision. — Organs  of  vision  have  been  figured  and  minutely  de- 


ORGANS  OF  SENSE.  57 

scribed  in  many  of  the  polygastric  animalcules  ;  they  vary  in  number 
from  one  in  the  polygastrics,  up  to  eight  in  the  acalepha.  In  the 
rotifera,  optic  nerves  and  ganglia  are  quite  visible,  and  in  the  aca- 
lepha a  lenticular  body  is  superadded.  Visual  organs  are  met  with 
in  almost  every  class  of  the  diplo-neurose  division  ;  in  some  there 
is  but  a  single  eye,  in  others  they  are  more  numerous,  and  placed 
apart  on  different  aspects  of  the  head.  The  medicinal  leech  pos- 
sesses ten  prominent  eyes  disposed  transversely,  and  the  neiris  nun- 
tia  has  two  large  pairs  placed  on  the  upper  part  of  the  head,  and 
nearly  a  hundred  smaller  ones  grouped  around  the  mouth.  Many 
of  the  higher  insects  present  in  their  optical  apparatus  all  the  essen- 
tial ingredients  found  in  the  highest  forms  of  the  organ.  The  eyes 
of  the  crustaceans,  are  generally  compound  like  those  of  insects,  and 
in  many  instances  are  moved  by  distinct  muscles,  and  covered  in 
front  by  a  transparent  layer  of  epidermis.  In  the  Crustacea,  as  in 
insects,  the  optic  nerves  enlarge  into  a  ganglion  in  the  globe  of  the 
compound  eye,  from  which  small  filaments  radiate  to  the  several 
lenses  of  the  component  eyes. 

Organs  of  vision  are  less  required,  and  consequently  less  deve- 
loped in  the  torpid  mollusca  than  in  the  active  articulata  ;  they 
never  form  groups  of  simple  eyes  like  the  myriapods,  nor  compound 
organs  like  the  insects  and  Crustacea.  In  the  acephalous  mollusca 
they  are  simple,  separate  and  numerous  as  in  worms,  but  in  the 
higher  forms  of  gasteropods,  pteropods,  and  so  on,  they  are  more 
complicated,  and  but  two  in  number,  disposed  on  the  sides  of  the 
head  as  in  the  vertebrata  ;  and  in  these  possessing  opaque  coverings, 
as  the  inhabitants  of  bivalve  shells,  they  are  altogether  wanting.  In 
those,  however,  which  enjoy  rapid  motion,  as  the  pectem  maximus, 
they  are  upwards  of  fifty  in  number,  each  being  about  a  quarter  of 
a  line  in  diameter.  The  eyes  of  these  animals  are  generally  flat- 
tened in  front,  they  possess  a  rudiment  of  membrana  nicitans;  the 
iris  and  the  lids  are  usually  motionless,  yet  in  the  general  plan  of 
their  formation  they  form  a  near  approach  to  the  condition  of  these 
organs  in  the  higher  vertebrated  classes. 

In  all  the  vertebrata  the  eyes  are  two  in  number,  and  with  the 
exception  of  a  few  species,  are  symmetrically  disposed  on  the  sides 
of  the  head  ;  the  differences  they  present  being  chiefly  referable  to 
the  density  of  the  media  in  which  the  various  animals  reside.  From 
the  density  of  the  watery  element  through  which  fish  move,  their 
eyes  are  generally  of  considerable  size,  except  in  the  worm-shaped 
fishes,  as  the  eel  and  the  lamprey.  Sometimes  they  are  directed 
backwards  or  upwards  as  in  the  star-gazer :  less  frequently  they  are 
placed  on  one  side,  as  in  the  sole.  The  eye  is  spherical  posteriorly, 
and  flattened  in  front.  The  conjunctiva  is  continued  across  in  front 
of  the  cornea,  and  admits  of  easy  separation  from  it  in  the  eel  and 
many  other  species.  The  eyelids  are  merely  rudimentary  and  the 
lachrymal  gland  is  wholly  absent.  The  sclerotic  tunic  is  thick, 
deuse,  laminated,  elastic,  and  occasionally  ossified  anteriorly.  The 
choroid  is  divisible  into  three  layers,  the  internal  or  tunica  Ruys- 


58 

chiaria,  the  middle  or  the  membrana  vasculosa  Halleri,  and  the 
external  with  its  shining  pearly  lustre  passes  in  front  of  the  iris 
and  produces  the  gold  and  silver  colours  so  much  admired.  The 
cornea  is  remarkable  for  its  flatness,  the  iris  for  its  immobility,  and 
the  crystalline  lens  for  its  density,  magnitude,  and  sphericity.  The 
aqueous  humour  is  scanty,  the  ciliary  processes  are  rarely  deve- 
loped, and  the  yellow  spot  of  Soemmerring  is  altogether  wanting. 
Between  the  layers  of  the  choroid,  and  embracing  the  optic  nerve,  a 
reddish  mass  of  a  horse-shoe  shape  is  found  in  most  fishes  named 
choroid  gland,  which,  according  to  some,  secretes  the  colouring 
matter ;  according  to  others  it  is  a  sort  of  rete  mirabile,  and  others 
again  look  upon  it  as  an  enlargement  of  the  optic  nerve,  whilst  the 
prevailing  opinion  at  present  seems  to  be,  that  it  is  a  muscle 
destined  to  modify  in  some  way  the  reflection  of  the  rays  of  light. 
From  the  inner  layer  of  the  choroid  another  body,  campanula 
Halleri,  passes  forwards  towards  the  lens,  somewhat  analogous  to 
the  marsupium  of  birds.  The  pupil  in  fishes  is  large  and  round, 
and  the  eye  is  moved  by  four  recti  and  two  obliqui  muscles. 

The  eyes  of  the  amphibia  are  very  large,  and  like  those  of 
fishes  contain  a  small  quantity  of  aqueous  humour,  and  are  flat  in 
front.  They  enjoy  great  latitude  of  motion  and  are  provided  with 
palpebrae  and  a  membrana  nictitans;  the  superior  lid  is  small  and 
scarcely  movable;  the  inferior  large  and  very  movable.  The 
opaque  integument  veils  the  front  of  the  eye  in  the  proteus ;  in 
most  other  characters  the  eyes  resemble  those  of  fishes. 

The  reptilia  present  us  with  characters  of  eyes  well  suited  to 
the  rare  medium  they  inhabit,  such  as  convexity  of  cornea  from 
abundance  of  humours,  and  a  compressed  state  of  the  lens.  .Like 
the  amphibia,  they  are  furnished  with  three  lids,  but  unlike  them 
and  fish,  they  are  provided  with  lachrymal  apparatus;  they  ap- 
proximate the  succeeding  classes  in  many  respects,  as  having  ciliary 
processes,  a  movable  iris,  generally  a  vertical  pupil,  a  dark  pecten 
prolonged  from  the  choroid  into  the  vitreous  humour,  and  osseous 
plates  around  the  anterior  margin  of  the  sclerotic.  In  the  chame- 
leon only  a  small  portion  of  the  eye  is  to  be  seen  through  a  narrow 
vertical  slit  between  the  margins  of  the  lids,  which  conceal  a  large 
membrana  nictitans. 

We  cannot  fail  to  observe  how  the  remarkable  peculiarities  pre- 
sented by  the  organs  of  vision  in  birds,  coincide  with  the  vigour  of 
their  respiratory,  circulatory,  and  locomotive  systems.  In  all  the 
other  vertebrate  classes  we  meet  with  instances,  where  the  eyes,  if 
not  absent,  are  at  least  rudimentary,  but  in  this  class  they  are 
remarkable  not  only  for  their  uniform  existence  but  for  their  great 
size  and  perfect  development.  From  the  convexity  of  the  anterior 
segment  of  the  eyes  and  their  lateral  location,  birds  command  an 
extensive  sphere  of  vision,  and  in  many  of  the  high-flying  rapa- 
cious kind,  the  orofan  is  prolonged  in  front  into  a  tubular  form,  but 
in  aquatic  birds  the  anterior  half  is  more  flattened.  The  sclerotic 
is  thin,  flexible,  and  elastic  posteriorly ;  it  is  divisible  into  three 


ORGANS  OF  SENSE.  59 

layers,  between  the  middle  and  outer  of  which,  from  15  to  17  osse- 
ous quadrangular  plates  are  placed  anteriorly,  a  repetition  of  what 
we  have  seen  in  reptiles  and  fishes;  these  scales  overlap  each  other, 
they  are  connected  by  the  sclerotic,  and  are  capable  of  a  limited 
degree  of  motion.  The  cornea  is  dense,  and  possesses  a  consider- 
able degree  of  convexity,  as  well  from  the  abundant  humours  as 
from  the  pressure  of  the  surrounding  muscles ;  and,  according  to 
the  discovery  of  Crampton,  it  is  capable  of  varying  its  convexity 
by  the  action  of  a  muscular  sphincter  attached  to  the  posterior 
layer  at  its  circumference.  The  choroid  is  the  same  as  in  mam- 
malia: the  iris  is  remarkable  for  the  freedom  of  its  motions  which, 
in  some  instances,  seem  voluntary:  the  pupil  is  generally  circular, 
but  elongated  transversely  in  the  goose  and  dove,  and  vertically 
oval  in  the  owl.  The  chief  peculiarity  in  the  eye  of  birds  consists 
in  the  marsupium  nigrum  or  pecten  plicatum  ;  this  wedge-shaped 
body,  which  in  appearance  simulates  choroid,  is  composed  princi- 
pally of  vessels,  and  extends  from  the  entrance  of  the  optic  nerve 
through  the  vitreous  humour  towards  the  lens  which  it  sometimes 
reaches,  and  gets  an  attachment  to.  Petit  supposed  that  this  sub- 
stance rendered  objects  in  front  of  the  eye  more  distinct  by  absorb- 
ing the  lateral  rays  of  light:  Home,  that  by  its  muscularity  it 
retracted  the  lens;  but  this  is  impossible  when  it  does  not  reach  it. 

Owen  considers  it  an  erectile  organ,  destined  to  push  forward 
the  lens  either  directly  or  through  the  medium  of  the  vitreous  hu- 
mour;  others  look  upon  it  as  a  gland  for  secreting  the  vitreous 
humour,  and  many  are  of  opinion  that  it  is  placed  there  for  the 
purpose  of  absorbing  the  super-abundant  rays  of  light  during  the 
exposure  of  the  eye  to  the  blazing  sun  when  soaring  aloft. 

The  aqueous  and  vitreous  humours  present  no  peculiarities  ; 
the  lens  is  flat  in  high-flying  birds  of  prey,  and  more  convex  in 
the  aquatic  species  ;  it  is  not  here  as  in  the  other  classes  an  achro- 
matic lens,  in  consequence  of  the  absence  of  central  nucleus.  The 
globe  of  the  eye  is  moved  by  four  recti  and  two  oblique  muscles. 
The  lower  lid  is  the  more  movable  in  birds  and  is  provided  with  a 
distinct  depressor  muscle.  The  third  eyelid,  or  membrana  nicti- 
tarts  is  a  conjunctival  fold  connected  with  the  inner  angle  of  the 
eye  and  capable  of  being  moved  across  the  organ  by  a  peculiar 
pair  of  muscles.  One  of  these,  from  its  shape,  is  named  quadratics  ; 
it  arises  from  the  upper  and  back  part  of  the  sclerotic;  its  fibris 
descend  in  a  convergent  manner  towards  the  optic  nerve,  a  little 
above  which  they  terminate  in  a  free  semilunar  aponeurotic  margin, 
containing  a  canal.  The  second  muscle  called  pyramidalis  arises 
from  the  inferior  internal  and  posterior  part  of  the  sclerotic,  its 
fibres  pass  converging  to  the  upper  surface  of  the  optic  nerve,  where 
it  forms  a  slender  tendon,  which  passes  though  the  canal  in  the 
quadratus;  it  then  passes  from  the  outer  to  the  lower  surface  of  the 
sclerotic,  conducted  in  a  cellular  sheath  till  it  gains  the  free  margin 
of  the  membrana  nictitans,  into  which  it  is  inserted. 

By  the  simultaneous  action  of  this  pair  of  muscles  the  membrane 


60  EVERS'S  COMPARATIVE  ANATOMY. 

is  rapidly  and  forcibly  drawn  downwards  and  outwards  over  the 
front  of  the  eye,  and  is  restored  to  its  former  situation  by  its  own 
elasticity.  The  lachrymal  gland  is  situated  at  the  external  angle 
of  the  eye,  and  at  the  internal  angle  there  is  another  gland  named 
Harderian,  from  its  discoverer,  but  is  nothing  more  than  a  con- 
geries of  mucous  follicles  to  compensate  for  the  absence  of  meibo- 
mian glands.  There  is  a  third  gland  in  or  near  the  orbit,  called 
nasal,  its  secretion  being  wholly  destined  for  the  nose. 

In  the  mammalia  the  organs  of  vision  are  Constructed  in  perfect 
accordance  with  the  media  the  animals  move  in  ;  they  are  usually 
placed  laterally,  but  in  the  nocturnal  quadrupeds  they  are  directed 
forwards  as  much  as  in  man,  and  in  the  quadrumana  even  more 
so.  The  eyes  are  of  a  large  size  in  ruminantia,  rodentia  and  many 
pachydermata;  and  they  are  small  in  moles,  shrews,  whales,  and 
in  most  cheiroptera.  In  the  mus  typhlus  the  eye  is  covered  by 
hairy  conjunctiva  ;  and  in  the  mole  of  Libanus,  it  is  so  small  as  to 
be  almost  invisible.  The  form  of  the  eye  is  generally  spherical, 
but  in  the  cetacea  flattened  anteriorly  as  in  fish,  and  in  bats  it 
approaches  to  that  of  birds.  In  the  cetacea  the  aqueous  and  vitre- 
ous humours  are  less  abundant  than  in  terrestrial  quadrupeds,  the 
cornea  is  flat,  the  lens  is  large,  dense,  and  round,  and  the  sclerotic  is 
an  inch  thick  posteriorly  in  a  whale,  with  an  eye  the  size  of  an 
orange;  the  lids  are  imperfectly  developed,  the  lachrymal  apparatus 
is  absent,  and  the  superior  oblique  muscle  of  the  eye  is  destitute  of 
a  pully ;  but  the  smallness  of  the  eye  in  this  order  of  mammalia, 
compared  wi  th  that  of  fish,  bespeaks  a  higher  development  of  internal 
perceptive  organs. 

In  the  carnivora  the  cornea  is  prominent,  the  pupil  vertically 
oval,  the  thick  choroid  without  pigmentum  nigum  posteriorly,  and 
a  blue  or  green  tapetum  glitters  in  the  bottom  of  the  eye.  The 
cornea  covers  half  the  eye  in  the  rat  and  porcupine,  and  is  elongated 
transversely  in  the  marmot,  and  generally  in  ruminants.  The 
tapetum  also  exists  in  the  ruminantia,  solipeda,  pachydermata,  and 
cetacea.  In  the  dog,  wolf,  and  badger  it  is  white,  bordered  by  blue. 
The  iris  is  subject  to  numerous  varieties  as  regards  its  colour, 
structure,  and  the  shape  of  the  pupil:  the  latter  is  of  a  circular 
form  in  the  rodentia,  bats,  and  simise ;  transversely  oval  in  the  ru- 
minantia, solipeda  and  cetacea  ;  in  these  instances  the  oval  form 
does  not  seem  to  pervade  the  entire  thickness  of  the  iris,  but  only 
its  external  layer.  The  retina  in  carnivora,  and  many  rodentia,  as 
in  some  birds,  is  confined  to  the  posterior  half  of  the  eye:  in  the 
former  on  account  of  the  breadth  of  the  corpus  ciliare ;  in  the 
latter  on  account  of  the  width  of  the  iris. 

In  the  mammalia  the  eyelids  are  formed  generally  as  they  are  in 
man,  the  superior  b«ing  the  larger  and  more  movable,  and  the 
membrana  nictitans  exist  in  the  entire  class,  with  the  exception  of 
man,  apes,  and  the  cetacea.  The  ornithorhynchus  histrix  has  but 
a  single  circular  lid.    In  addition  to  the  lachrymal  gland,  which  is 


ORGANS  OF  SENSE.  61 

found  in  all  mammalia,  except  the  cetacea,  the  glandula  Harden 
exists  in  the  carnivora,  ruminantia,  pachydermata,  and  some  roden- 
tia.  Instead  of  puncta  lachrymalia,  the  hare  and  rabbit  have  a  slit 
opening  into  the  nasal  duct ;  the  eye  is  moved  by  four  recti  and 
two  oblique  muscles,  and  in  many  of  the  genus  felis  the  superior 
oblique  is  perforated  by  the  rectus  superior :  the  inferior  oblique 
has  the  same  relation  to  the  inferior  rectus  in  the  tiger,  though  not 
in  the  lion.  All  the  muscles  of  the  eye  are  said  to  be  wanting  in 
those  animals  in  which  the  organ  is  in  a  rudimentary  state. 

Hearing. — When  we  consider  the  many  services  arising  from 
this  sense,  such  as  indicating  the  approach  of  danger,  conducting 
predaceous  animals  to  their  prey,  the  bringing  together  the  two  sexes, 
(fee,  we  should  expect  to  find,  as  we  really  do,  an  organ  of  hearing 
in  almost  every  division  of  the  animal  kingdom.  In  the  radiated 
division  of  animals  no  distinct  acoustic  organs  have  been  detected ; 
it  is  probable,  however,  that  the  undulations  produced  by  the  per- 
cussion of  outward  bodies  in  the  media  in  which  these  low  creatures 
reside,  produce  some  impression,  though  feeble  it  may  be,  upon  the 
general  surface  of  their  bodies.  It  is  not  till  we  ascend  in  the  scale 
as  high  as  the  active  air  breathing  insects  of  the  articulata  that  we 
meet  with  special  organs  appropriated  to  this  sense  ;  and  here  they 
consist  of  auditory  nerve,  vestibule,  and  two  rudimentary  semicir- 
cular canals.  In  many  of  the  inferior  torpid  mollusca  there  do  not 
seem  to  be  any  particular  organs  devoted  to  the  perception  of  sound, 
but  in  the  higher  cephalopods  which  approach  the  nearest  to  fish 
in  their  general  characters,  the  organs  of  hearing  present  a  similar 
degree  of  complexity. 

Fishes,  like  the  cephalopodous  mollusca,  receive  their  acoustic 
impression  by  undulations  through  the  dense  medium  surrounding 
them,  and  in  the  lowest  cartilaginous  species,  as  the  lamprey,  the 
organ  consists  of  a  simple  vestibule,  and  three  membranous  semi- 
circular canals,  separated  from  the  cavity  of  the  skull  merely  by 
dura  mater.  In  the  bony  fishes  the  vestibule  and  semicircular 
canals  are  highly  developed,  fenestra  ovalis  appears,  and  by  and  by 
a  rudimentary  cochlea  and  tympanum  without  air  are  seen  ;  in  the 
cavity  of  the  vestibule  two  or  three  small  bodies  are  found,  soft  and 
pulpy  in  the  cartilaginous  fishes,  but  of  a  stony  hardness  in  the 
osseous  kind,  and  composed  of  carbonate  of  lime. 

In  the  aquatic  amphibia  and  in  the  tadpole  state  of  the  reptiliform 
species,  the  organ  of  hearing  possesses  a  near  affinity  to  that  of 
fishes  ;  it  consists  of  the  vestibular  cavity  containing  its  cretaceous 
bodies,  the  membranous  semicircular  canals,  and  fenestra  ovalis 
closed  by  stapes,  all  contained  in  a  cavity  of  the  temporal  bone,  and 
covered  externally  by  the  common  integument.  But  in  the  adult 
state  of  the  frog  and  salamander  the  apparatus  is  more  complicated, 
the  semicircular  canals  are  lodged  in  the  temporal  bone  ;  the  tym- 
panum is  closed  by  membrana  tympani,  contains  three  ossicula 
united,  and  communicates  with  the  fauces  by  a  Eustachian  tube. 

The  reptiles  present  a  higher  development  of  acoustic  organs  ;  in 


62 

serpents,  however,  they  closoly  resemble  the  caduci-branchiate  am- 
phibia, and  by  their  vestibular  saculus,  containing  solid  cretaceous 
bodies,  they  resemble  the  osseous  fishes.  The  cavity  of  the  tym- 
panum is  larger  in  the  saurian  than  in  the  ophidian  reptiles.  As 
we  ascend  to  the  higher  orders,  we  meet  with  a  cochlea,  which  is 
the  last  part  of  the  internal  ear  that  attains  perfection,  slightly  cnrved 
and  divided  into  a  scala  tympani  and  scala  vestibuli. 

In  birds  the  organ  of  hearing  resembles  that  of  the  crocodile  ; 
there  is  no  cartilaginous  external  ear,  and  but  a  rudimentary  concha, 
which,  however,  is  compensated  for,  especially  in  rapacious  birds, 
by  a  peculiar  arrangement  of  feathers  around  the  external  meatus, 
which  in  general  they  can  erect  at  will  so  as  to  catch  distant  sounds, 
and  by  that  means  either  flee  from  danger,  or  pursue  their  prey 
through  dark  and  gloomy  places.  The  external  ear  of  owls  is  fur- 
nished with  a  crescentic  fold  of  integument  in  the  form  of  a  valve. 
The  oval  tympanum,  surrounded  by  bone,  communicates  with  the 
air-cells  of  the  cranium  by  three  large  openings,  and  with  the 
fauces  by  two  short  wide  Eustachian  tubes  which  open  by  a  single 
orifice  in  the  swan  at  the  back  of  the  posterior  nares.  There  is  but 
one  bone  in  the  tympanum  analogous  to  the  stapes,  with  processes 
rudimentary  of  the  malleus  and  incus,  and  moved  by  a  single  tensor 
muscle,  which  comes  from  the  occiput  and  increases  the  convexity 
of  the  membrana  tympani  by  drawing  it  outwards.  The  cochlea, 
though  more  developed  than  in  reptiles,  has  not  yet  reached  perfec- 
tion, and  the  other  parts  of  the  internal  ear  present  no  remarkable 
peculiarities  different  from  the  inferior  grades  of  the  next  class. 

In  the  mnmmalia,  generally,  the  organ  of  hearing  is  distinguished 
by  the  development  of  a  true  cochlea  ;  by  an  increased  number  of 
auditory  hones ;  by  the  formation  of  external  canal,  and  by  the 
addition  of  an  external  movable  ear.  We  will  meet,  however,  with 
evident,  though  gradual,  transitions  from  the  simple  state  of  organ 
already  seen  in  the  inferior  classes,  up  to  man,  where  it  has  attained 
its  most  complex  and  perfect  condition.  The  concha  is  very  small 
in  otarite,  beavers,  and  otters,  and  wholly  absent  in  the  cetacea, 
seals,  walruses,  the  mole,  the  manis,  and  the  ornithorhynchus.  The 
aquatic  shrew  and  other  mammalia  which  frequently  go  into  the 
water,  form  an  approach  to  the  crocodlile  in  having  the  external 
auditory  opening  furnished  with  a  valve.  This  external  orifice  in 
the  dolphin  is  merely  large  enough  to  admit  a  pin,  and  from  it  a 
long  narrow  winding  passage  leads  to  the  tympanum  through  the 
fat  which  lies  under  the  skin.  As  we  ascend  through  the  mam- 
malia, residing  more  exclusively  on  the  land,  the  concha  acquires 
greater  size,  and  by  the  development  of  cartilage  and  powerful 
muscles  it  becomes  to  enjoy  very  free  and  varied  motions.  It  is 
large,  movable,  and  directed  backwards  in  the  ruminantia,  pachy- 
dermata,  cheiroptera;  and  especially  in  the  timid  and  feeble  rodentia ; 
and  in  the  carnivora  it  is  small  and  inclined  forwards. 

The  cavity  of  the  tympanum  communicates  with  the  mastoid  cells, 
contains  four  movable  ossicula  and  three  distinct  muscles ;  it  is 


ORGANS  OF  SENSE.  63 

closed  by  a  raembrana  tympani,  which  is  concave  externally,  except 
in  the  whale.  In  the  ornithorhynchus,  which  in  so  many  points  of 
view  constitutes  the  connecting  link  between  reptiles  and  the  higher 
classes  of  animals,  the  external  passage  is  long  and  singularly  tor- 
tuous, the  ossicula  auditus  anchylosed,  the  cochlea  represents  a 
curved  horn,  as  in  birds  and  reptiles,  and  the  semicircular  canals 
project  into  the  cranium.  The  Eustachian  tube  is  wide  in  the  ceta- 
cea,  it  opens  at  the  blowing  hole,  where  it  is  furnished  with  a  valve; 
the  cochlea  is  short  and  convoluted  in  one  plane  in  the  cetacea,  long, 
narrow,  and  spiral  in  the  rodentia,  and  in  the  guinea-pig,  porcupine, 
and  aguti,  it  forms  three  turns  and  a  half;  the  other  essential  parts 
of  the  labyrinth  agree  on  the  whole  with  those  of  the  human 
subject. 

Smell. — No  organs  subservient  to  this  sense  have  been  detected 
in  the  cyclo-neurose  animals,  but  in  the  annelidesof  the  diplo-neura, 
the  sense  is  said  to  reside  in  the  parietes  of  their  mouths,  or  the  pores 
of  their  air-sacs,  and  in  the  palpi,  and  autennag  of  insects.  The 
entrance  to  the  respiratory  passages,  the  sensitive  tentacula,  and 
even  the  whole  surface  of  the  body  in  the  higher  orders  of  the  mol- 
lusea,  are  capable  of  receiving  odorous  impressions.  The  lami- 
nated organs  of  smell  in  fishes  are  placed  in  two  small  depressions  on 
the  anterior  part  of  the  face ;  they  are  protected  by  cartilage,  lined 
by  a  delicate  mucous  membrane  disposed  in  radiated  folds  in  the 
pike:  tufted  in  the  cyprinus,  and  arranged  like  the  barbs  of  a  quill 
in  the  carp,  ray,  and  shark.  These  cavities  have  no  communication 
with  the  mouth  or  pharynx ;  they  are  closed  in  front  by  a  valve 
formed  of  skin  and  cartilage,  and  a  similar  structure  partly  divides 
each  into  two. 

In  the  perennibranchiate  amphibia,  as  the  proteus  and  siren,  the 
organs  of  smell  in  every  respect  resemble  those  of  fishes,  and  in  the 
more  highly  developed  genera,  as  frogs  and  salamanders,  they 
approach  in  characters  to  those  of  reptiles.  The  nostrils  are  partly 
cartilaginous,  partly  osseous,  and  open  into  the  cavity  of  the  mouth. 
The  olfactory  nerves  enter  by  two  foramina  in  the  ethmoid  bone, 
and  are  distributed  to  every  part  of  the  soft  pituitary  membrane.  In 
serpents  the  nasal  cavities  present  rudimentary  turbinated  bones, 
and  open  posteriorly  by  a  single  orifice.  The  turbinated  bones  are 
larger  and  more  curved  in  the  sauna,  and  in  the  chelonia  the  olfac- 
tory surface  is  greatly  extended  and  concealed  by  a  strong  osseous 
covering. 

In  birds  the  external  nostrils  vary  much  as  to  size,  shape,  and 
situation,  they  are  generally  free  and  wide,  but  in  some  instances 
very  small,  as  in  the  heron  and  gannet.  The  septum  narium  is 
partly  bony,  partly  cartilaginous,  and  covered  by  a  highly  vascular 
pituitary  membrane  in  the  swan.  The  nasal  cavities  in  birds  con- 
tain three  turbinated  bones  and  open  separately  into  the  pharynx, 
except  in  the  cormorant,  where  they  join  previous  to  their  opening. 
The  olfactory  nerves  are  distributed  exclusively  to  the  membrane 
covering  the  septum  narium  and  superior  spongy  bone.    It  is  gene- 


64  EVERS'S  COMPARATIVE  ANATOMY. 

rally  supposed  that  birds  of  prey  are  gifted  with  an  acute  sense  of 
smell,  but  the  experiments  of  Mr  Audubon  go  to  prove  the  reverse 
opinion  ;  and  according  to  the  researches  of  Scarpa,  the  following  is 
the  order  in  which  it  is  enjoyed,  beginning  with  those  in  which  it 
is  most  acute ;  grallatores,  natatores,  raptor  es,  scansores,  inses- 
sores,  rasores. 

The  organs  of  smell  in  the  mammalia  are  distinguished  by  the 
more  perfect  formation  of  external  nose,  by  the  large  size  of  the 
nasal  cavities,  and  by  the  latter  receiving  several  new  openings, 
such  as  the  frontal,  nasal,  ethmoidal,  sphenoidal,  and  maxillary 
sinuses.  The  external  openings  are  valvular  in  the  beavers,  seals, 
and  camels,  and  variously  modified  in  other  animals,  according  to 
their  different  habits,  as  in  the  hog,  elephant,  &c.  The  turbinated 
bones  are  long  and  simple  in  the  rodentia,  ruminanlia,  and  pachy- 
dermata,  and  they  form  a  complicated  series  of  labyrinths  in  the 
carnivorous  tribes,  where  an  acute  sense  is  so  necessary  to  enable 
them  to  pursue  their  prey  through  their  dark  retreats.  The  large 
olfactory  nerves  pass  through  the  numerous  openings  of  the  cribri- 
form plate,  except  in  the  cetacea,  to  be  distributed  on  the  surface  of  the 
turbinated  bones.  These  nerves  are  large  and  hollow  in  the  human 
foetus,  like  the  olfactory  tubercles  of  quadrupeds,  and  it  is  interest- 
ing to  observe  how  the  sense  of  smell  preponderates  over  all  others 
in  the  new  born  child,  this  can  be  easily  tested  during  the  nuzzling 
of  the  infant  at  the  mother's  breast,  when  the  loudest  sounds  may 
assail  its  ears  without  effect,  and  when  its  visual  powers  are  limited 
to  the  mere  perception  of  intense  light. 

Taste. — A  considerable  degree  of  obscurity  prevails,  respecting 
the  enjoyment  of  this  sense  in  the  different  classes  of  animals,  and 
although  we  cannot  display  any  organ  especially  appropriated  to  it 
in  the  inferior  tribes  of  animals,  yet  it  is  supposed  that  all  enjoy  it, 
from  the  polygastric  animalcules  up  to  man.  It  is  generally  seated 
in,  but  by  no  means  confined  to  the  tongue,  this  organ  being  absent 
in  some  instances  even  in  the  human  subject,  where  the  existence 
of  the  sense  has  been  proved;  and  in  other  cases,  where  the  tongue 
does  exist,  its  dense  horny  nature  excludes  it  from  such  an  enjoy- 
ment. The  form  of  the  tongue  differs  considerably  in  different 
animals;  in  none,  not  even  in  the  simiae,  is  it  exactly  like  that  of 
man.  In  the  cephalopoda  distinct  gustatory  villi  cover  its  surface ; 
in  many  fishes  it  has  no  papillae,  and  in  others  it  is  set  with  teeth ; 
in  the  chameleon  it  is  an  organ  of  very  peculiar  mechanism,  and 
admits  of  being  protruded  for  several  inches  in  pursuit  of  prey,  with 
amazing  celerity  and  precision.  This  power,  for  a  long  period  a 
paradox  with  naturalists  was  discovered  by  Dr.  Houston  to  be  of  an 
erectile  nature.  In  birds  it  serves  chiefly  as  an  organ  of  prehension, 
in  a  few  only  does  it  possess  papillae,  being  generally  sheathed  in 
front  by  horn.  With  few  exceptions  among  the  edentata,  the 
tongue  in  the  mammalia  serves  as  an  organ  of  taste.  In  the  bisulca 
it  is  covered  with  a  thick  epithelium ;  in  the  bat,  the  opossum,  and 


ORGANS  OF  SENSE.  65 

especially  the  lion,  and  others  of  the  cat  kind,  it  is  beset  with  strong 
sharp  prickles,  for  prehensile  purposes. 

Touch. — This  is  the  most  general  as  well  as  the  most  simple  of 
the  senses,  and  the  degree  in  which  it  exists  has  reference  to  the 
state  of  the  tegnmentary  membrane,  and  I  he  condition  of  the  nervous 
system.  In  the  invertebrata  no  organs  solely  devoted  to  the  per- 
ception of  sensitive  impressions  have  been  detected,  yet  there  is  little 
doubt  but  that  the  cilia  of  most  poly  wastries,  the  ten  taenia  of  zoo- 
phytes and  mollusca,  and  the  antennas  of  ray  ri  a  pods  and  insects  are 
subservient  to  this  sense.  Some  fishes  have  fleshy  sensitive  fila- 
ments arranged  around  the  month  after  the  manner  of  ten  taenia, 
and  others  have  only  the  skin  on  the  abdomen,  or  about  the  mouth, 
uncovered  with  scales,  and  capable  of  receiving-  external  impres- 
sions. The  tongue  among  serpents,  and  the  tail  among  saurian 
reptiles,  and  some  mammalia,  constitute  their  chief  tactile  organs. 
The  organs  of  touch  in  birds  are  the  bills,  the  cire  in  the  falconidce 
the  wattles  of  the  cock,  and  the  caruncles  of  the  turkey.  It  must 
be  acknowledged,  however,  that  this  sense  is  very  limited  in  birds, 
which  is  in  some  degree  compensated  for  by  the  free  distribution  of 
the  fifth  pair  of  nerves  to  their  horny  bills,  especially  those  of  the 
aquatic  species,  which  procure  their  aliment  from  mud. 

In  many  of  the  mammalia  the  skin  is  shielded  from  external  im- 
pressions by  the  presence  of  horny  or  spiny  coverings,  dense  furs. 
or  thick  hides;  and  it  is  not  till  we  arrive  at  the  higher  orders  of 
quadrupeds,  carnivora  and  quadrumana,  that  the  organ  of  touch 
makes  any  approach  to  the  perfect  development  of  it  observed  in 
the  human  subject. 

RECAPITULATION. 

1.  Organs  of  vision  exist  in  every  class  of  animals,  and  in  the 
lowest  orders  the  eyes  vary  in  number  from  one  to  near  100. 

2.  In  the  vertebrata  the  eyes  are  two  and  vary  much  in  form  and 
situation. 

3.  No  organs  of  hearing  or  smell  have  been  detected  in  the 
radiata. 

4.  Our  knowledge  concerning  the  organ  of  taste  is  involved  in 
much  obscurity. 

5.  No  organ  of  touch  has  been  detected  in  the  invertebrata. 


CHAPTER.  X 

ORGANS  OF  DIGESTION   IN  THE  INVERTEBRATA. 

General  observations. — The  organs  engaged  in  the  function  of 
digestion    may  be  arranged  under   two   heads:   the   primary,  or 
8 — f  evers  5 


66  EVERS'S  COMPARATIVE  ANATOMY. 

essential — including  the  alimentary  tract;  and  the  secondary,  or 
tributary,  embracing  the  liver,  spleen,  pancreas,  salivary,  and 
mucous  glands. 

There  is  no  organ  so  universally  present,  nor  so  essential,  as  an 
internal  digestive  cavity,  and  hence  so  often  alluded  to  as  consti- 
tuting a  line  of  distinction  between  the  animal  and  the  vegetable 
kingdoms ;  indeed  there  is  no  class  of  animals  without  it,  although 
it  is  not  found  in  every  species  of  each  class.  The  peculiarities 
presented  by  the  digestive  apparatus  will  vary  according  to  the 
rank  an  animal  holds  in  the  scale  of  the  creation,  the  kind  of  food 
on  which  it  is  destined  to  subsist,  and  the  elaboration  that  food 
may  require  to  undergo.  The  alimentary  surface  of  a  plant  is  the 
exterior  of  its  root  spread  out  in  the  earth,  and  absorbing,  by  its 
spongioles,  the  materials  for  its  nutrition,  but  the  alimentary  surface 
of  an  animal  is  internal,  and  continued  from  the  skin,  like  the  in- 
side of  a  lady's  muff. 

Cyclo-neura,  Grant — Radiata,  Cuvier. —  In  the  very  low 
tribes  of  animals  the  digestive  apparatus  presents  characters  equally 
diversified  as  the  forms  of  the  creatures  themselves.  The  aliment- 
ary cavity  has  often  but  one  orifice;  there  are  seldom  teeth  or 
glandular  organs,  and  the  food  is  generally  of  the  simplest  sort.  In 
the  polygastrica,  as  the  term  signifies,  the  cavities  are  numerous, 
and  their  various  forms  have  been  well  observed  by  Ehrenberg, 
who  caused  these  transparent  animalcules  to  swallow  fluids  coloured 
with  carmine,  indigo,  or  sap-green.  The  monads  and  several  other 
genera  have  but  one  orifice  which  receives  the  openings  of  the  several 
cavities,  and  from  the  absence  of  intestine  the  entire  group  has  been 
named  anentera.  in  the  higher  forms,  however,  the  alimentary 
canal  is  furnished  with  an  oral  and  an  anal  orifice,  the  straight, 
curved,  or  spinal  intestine  receives  the  openings  of  numerous  ccecal 
appendices  through  its  whole  course.  In  some  of  the  small  monads 
no  internal  cavity  has  been  detected,  and  in  other  genera  the  num- 
ber varies  from  one  up  to  two  hundred,  as  seen  in  a  paramascium. 
Many  species  are  provided  with  dental  organs  in  the  form  of  stiff 
spines  disposed  around  the  mouth,  but  in  none  of  the  class  have 
tributary  or  glandular  organs  been  observed. 

The  porifera  present  a  very  simple  form  of  alimentary  appa- 
ratus, their  absorbent  canals  closely  resembling  the  ramified  roots 
of  plants,  and  as  we  ascend  through  the  diversified  series  of  the 
polypifera  or  zoophytes  we  perceive  the  system  increasing  in  com- 
plexity from  the  simple  genito-digestive  sac  of  the  hydra  up  to  the 
complicated  structure  presented  by  the  actiniform  polypi,  where  the 
stomach  is  provided  with  a  muscular  and  mucous  tunic  lined  with, 
vibralile  cilia,  and  communicates  inferiorly  with  the  genital  cavities. 
The  greater  number  of  the  acalepha  possess  a  simple  broad  and 
radiated  alimentary  cavity,  suited  to  their  highly  organised  and 
minutely  divided  food,  but  in  the  monostomatous  species,  which 
live  on  coarser  aliment,  a  cartilaginous  masticatory  apparatus  and 
biliary  secretion  are  superadded.     The  torpid  predaceous  echino- 


ORGANS  OF  DIGESTION  IN  THE  INVERTEBRATA.  67 

dermata  afford  in  the  structure  of  their  digestive  organs,  connecting 
links  of  transition  from  the  radiated  to  the  articulated  classes.  In 
the  higher  forms  of  the  echinida  strong  masticating  and  salivary- 
organs  are  provided,  the  anal  orifice,  which  in  the  lower  tribes  is 
placed  on  the  inferior  surface,  gains  a  dorsal  aspect,  which  it  con- 
tinues to  hold  in  the  holothuriae  and  articulated  classes.  Thus  we 
perceive  the  digestive  cavity,  from  being  a  simple  monostome  sac, 
gradually  acquires  the  form  of  a  long  narrow  canal,  open  at  both 
ends,  and  furnished  with  salivary  and  biliary  organs. 

Diplo-neura,  Grant — Articulate  Cuvier. — The  carnivorous 
character  of  this  great  division  of  the  animal  kingdom  bespeaks  an 
alimentary  canal,  limited  in  its  capacity,  straight  in  its  form,  and 
simple  in  its  structure.  This  canal  usually  takes  a  horizontal 
direction,  opens  at  the  two  opposite  extremities  of  the  body,  and  is 
provided  at  its  commencement  with  prehensile,  destructive,  or  mas- 
ticating organs.  In  consequence  of  the  simple  nature  of  the  food 
on  which  the  entozoa  subsist,  many  of  them  have  but  a  single  orifice 
to  their  digestive  sac.  In  the  higher  and  more  perfect  forms,  how- 
ever, of  these  as  well  as  of  the  rotifer  a,  the  canal  passes  straight 
or  slightly  winding  through  the  body,  presenting  an  oral  and  anal 
aperture,  and  surrounded  by  the  genital  and  biliary  organs.  The 
cirrhopoda  are  remarkable  for  the  great  size  of  their  salivary  and 
biliary  apparatus,  and  the  wide  ducts  of  the  latter,  which  open  into 
the  stomach,  as  in  most  of  the  invertebrated  tribes. 

Among  the  annelida  the  earth-worm  is  remarkable  for  its  capa- 
cious mouth,  a  small  salivary  gland,  a  sacculated  stomach,  consist- 
ing of  three  continuous  cavities,  and  a  narrow,  slightly  bending 
intestine.  The  leech  has  three  horny  maxillae,  furnished  with  sharp 
teeth,  with  which  it  inflicts  its  tri-radiate  wound,  the  straight,  irre- 
gularly sacculated  intestine  is  furnished  with  ten  pairs  of  lateral 
coeca,  and  enlarges  into  a  small  sac  near  ihe  anus.  The  carnivo- 
rous rnyriapods  are  provided  with  three  pairs  of  salivary  and  two 
poison-glands,  by  their  contracted  oesophagus  and  elongated  mem- 
branous stomach,  they  resemble  the  higher  species  of  worms,  and 
by  their  small,  narrow  intestine,  ending  in  a  wide  colon,  they  are 
allied  to  the  ophidian  reptiles. 

The  digestive  organs  of  the  insecta  present  in  an  embryo  state 
nearly  all  the  essential  elements  of  the  chylo-poietic  system  in  the 
highest  classes  of  animals,  as  masticating  organs,  salivary  and 
mucous  glands,  liver,  pancreas,  &c. :  they  will  be  found  to  vary, 
however,  according  to  the  peculiar  living  habits  of  the  species,  and 
the  quality  of  their  food.  The  alimentary  canal  usually  consists 
of  a  wide  pharynx,  a  narrow  oesophagus,  a  dilated  crop,  a  muscular 
gizzard,  provided  with  sharp,  conical,  horny  teeth,  a  capacious  chy- 
lific  stomach,  a  straight,  narrow  intestine,  a  short,  dilated  colon, 
and  a  contracted  cloaca.  In  the  herbivorous  insects,  the  alimentary 
canal  is  long,  capacious,  and  complicated.  The  gall-bladder  is 
usually  single,  but  occasionally  double.  The  cunning  carnivo- 
rous aracknida  resemble  the  insects  in  the  arrangement  of  their 


68 

masticating  organs,  whilst  their  straight  narrow  alimentary  canal 
and  the  compact  state  of  their  liver,  ally  them  to  the  Crustacea. 

Like  most  other  carnivorous  articulata,  the  cunning,  cruel, 
aqautic  crustaceans  are  provided  with  prehensile  and  masticating 
organs  well  suited  to  destroy  the  prey  in  the  rich  element  they  in- 
habit. The  maxillae  vary  from  one  to  five  pairs,  but  are  wanting 
in  the  lower  orders.  The  alimentary  canal  is  generally  without 
convolutions,  and  opens  by  two  apertures.  The  decapods  present 
a  narrow  oesophagus,  leading  to  a  capacious  muscular  stomach, 
furnished  with  numerous  solid  calcarious  teeth,  and  a  straight  in- 
testine occupying  the  dorsal  portion  of  the  trunk,  and  receiving- 
near  its  commencement  the  biliary  and  pancreatic  ducts.  The 
salivary  glands  are  absent  except  in  the  higher  orders,  where  rudi- 
ments of  them  are  perceived  surrounding  the  oesophagus.  The 
mucous  membrane  forms  rugae  in  the  oesophagus  and  stomach, 
but  not  in  the  intestine,  and  the  peritoneum  ibrms  no  mesentery. 

Cyclo-gangliata,  Grant — Mblluscq,  Cuvier. — This  great  divi- 
sion of  the  animal  kingdom  being  destined  chiefly  to  subsist  on 
soft  food,  masticating  organs  are  little  required  by  them,  hence  they 
are  often  but  sliohtly  developed,  and  in  some  cases  wholly  absent. 
But  their  food  is  greatly  varied  and  often  coarse,  so  as  to  require  a 
complicated  form  of  alimentary  canal,  and  a  high  development  of 
glandular  apparatus.  The  digestive  organs  of  the  tunica t a  closely 
resemble  those  of  the  conchifcra,  being  a  little  more  complicated  in 
the  latter.  Both  are  destitute  of  prehensile  or  masticating  organs, 
and  depend  for  their  supply  of  food  on  the  respiratory  currents. 
They  possess  a  short  wide  oesophagus,  opening  into  a  capacious 
muscular  stomach,  without  teeth,  and  receiving  the  biliary  ducts. 
The  intestine  is  generally  short,  wide,  and  convoluted.  The  con- 
chifera  differ  from  the  tunicata  by  their  long  and  convoluted  intes- 
tine passing  between  the  two  aorta?,  through  the  fleshy  substance 
of  the  ventricle,  and  the  mass  of  the  liver.  The  terrestrial  pulmo- 
nated  gasieropnds  present  a  more  complicated  digestive  apparatus 
than  the  acephalous  mollusca,  especially  those  which  feed  on  vege- 
table substances.  They  are  provided  with  a  pair  of  horny  jaws,  a 
muscular  tongue  and  proboscis  armed  with  sharp  recurved  spines,  a 
large  pharynx,  a  long  oesophagus,  and  a  capacious  stomach,  divided 
in  the  phytophagous  species,  into  several  compartments,  fur- 
nished internally  with  teeth,  and  receiving  the  biliary  and  pancre- 
atic secretions.  One  or  two  pairs  of  salivary  glands  lie  around  the 
oesophagus,  and  the  liver  is  of  considerable  size.  The  intestine 
is  long  and  convoluted,  and  opens  in  common  with  the  genital  or- 
gans on  the  right  side,  near  the  anterior  extremity  of  the  body.  In 
the  pteropods  and  cephahpods,  the  oesophagus  passes  through  the 
cranial  cartilage  and  ganglionic  ring,  sometimes  dilating  into  a 
crop  before  entering  the  muscular  gizzard,  which  is  often  lined 
with  a  thick  coriaceous  epithelium.  The  intestine  is  short  and 
wide  in  the  carnivorous  species,  destitute  of  coecum-coli,  not  dis- 
tinguished into  large  and  small  as  in  the  vertebrata,  and  no  where 


VERTEBRATA.  69 

imbedded  in  the  substance  of  the  liver,  as  in  many  of  the  inferior 
mollusca.  The  mollusca  are  without  gall-bladder^  and  as  yet  no 
portal  circulation  has  appeared.  The  entrance  of  the  hepatic  duct 
into  the  stomach  is  guarded  by  a  pair  of  prominent  valves,  pro- 
longed so  into  the  intestine  as  to  allow  of  the  passage  of  the  pan- 
creatic and  biliary  secretions  into  the  gut  during  a  state  of  vacuity 
without  entering  the  stomach  or  duodenum. 


CHAPTER  XI. 

VERTEBRATA. 

In  this  great  department  of  the  animal  world  the  digestive  appa- 
ratus presents  a  higher  development  and  a  greater  degree  of  com- 
plexity than  we  have  met  with  before.  The  alimentary  canal 
always  swells  out  into  a  distinct  gastric  enlargement,  and  is  provided 
with  a  large  conglomerate  liver,  spleen  and  pancreas.  The  duode- 
num invariably  receives  the  biliary  and  pancreatic  secretions,  and 
he  salivary  glands  are  rarely  absent.  The  teeth  are  generally 
confined  to  the  alveoli,  and  there  are  none  found  in  the  stomach. 
As  a  general  rule  the  canal  is  longer,  larger  and  more  sacculated, 
and  the  masticating;  and  glandular  apparatus  more  developed  in 
the  phytophagous  than  in  the  carnivorous  tribes. 

PISCES. 

Since  vegetable  food  cannot  be  procured  in  the  unfathomable 
depths  of  the  sea,  we  are  prepared  to  meet  with  a  short  and  simple 
form  of  alimentary  canal  in  fishes,  suited  to  their  predaceous  habits. 
Vegetable  substances  might  even  endanger  their  lives  by  an  evolu- 
tion of  gas  which  would  render  them  specifically  lighter  than  the 
water,  and  cause  them  to  float  upon  its  surface  with  the  belly  up- 
wards. The  teeth  of  fishes  are  generally  numerous,  destitute  of 
fangs,  laminated,  deciduous,  thinly  covered  with  enamel,  and 
movable  on  the  surface  to  which  they  adhere,  till  maturity,  when 
they  become  permanently  fixed.  The  teeth  of  fishes  are  often 
implanted  in  the  tongue  as  in  many  gasteropods  and  birds,  in  the 
vomer  as  in  amphibia,  in  the  palate  bones  as  in  serpents,  in  the 
pharyngeal  bones,  branchial  arches  and  os  hyoides,  as  well  as  in  the 
maxillary  and  inter-maxillary  bones  to  which  they  are  confined  in 
the  saurian  reptiles  and  mammalia;  the  teeth  are  most  numerous 
in  the  pike  and  salmon,  and  are  altogether  wanting  in  some  genera, 
as  the  sturgeon.  As  in  serpents,  crocodiles,  dolphins,  and  other 
predaceous  non-masticating  vertebrata,  the  teeth  are  not  opposed  to 
each  other  but  placed  alternately,  adapting  them  to  their  prehensile 
office. 


70 

The  tongue  is  broad,  short,  and  almost  destitute  of  papillae.  The 
salivary  glands  are  only  rudimentary,  and  even  wanting  where  the 
liver  and  pancreas  are  well  developed,  but  the  mouth  is  well  sup- 
plied with  mucus.  The  short,  wide  infundibuliform  oesophagus 
has  an  external  circular,  and  an  internal  longitudinal  layer  of  mus- 
cular fibres,  and  is  lined  with  a  pale,  villous,  longitudinally  plicated 
mucous  membrane  provided  with  numerous  mucciperous  follicles. 
The  large  gastric  cavity  is  sometimes  long  and  tapering  as  in  the 
herring,  and  sometimes  globular  as  in  the  lophius:  its  two  orifices 
are  closely  approximated,  so  that  the  food  is  retained  in  it  for  a  long 
period,  hence,  if  we  feed  a  tame  perch  till  it  is  gorged,  it  will  not 
eat  again  for  ten  or  fourteen  days ;  both  orifices  of  the  stomach  are 
sphinctorial,  its  mucous  membrane  is  plicated  and  forms  a  valve  at 
the  pylorus  with  a  fringed  margin,  surrounded  by  a  ring  of  carti- 
lage. The  intestine,  in  many  cases,  does  not  measure  more  than 
half  the  length  of  the  body,  in  others,  however,  as  the  sword  fish,  it 
forms  several  convolutions,  but  rarely  does  it  admit  of  any  distinc- 
tion into  large  and  small.  In  the  sturgeon,  ray,  and  shark  the  anal 
is  smaller  than  the  cardiac  portion,  and  the  reverse  obtains  in  the 
pleuronectes,  gadi,  murcenae,  &c.  In  order  to  compensate  for  the 
shortness  of  the  canal  and  the  absence  of  valvulse  conniventes,  the 
lining  membrane  is  peculiarly  disposed,  being  reticulated  in  the 
sturgeon,  forming  spiral  turns  in  the  shark  and  ray,  and  serpentine 
folds  in  the  eel.  The  rectum  here  as  in  oviparous  vertebrata,  ter- 
minates in  the  cloaca  through  which  are  discharged  feces,  urine, 
semen,  and  ova.  On  either  side  of  the  anus  there  is  an  oblique 
valvular  opening,  admitting  of  free  egress,  but  prohibiting  any 
thing  from  without,  and  the  air-sac,  or  rudimentary  lung  commu- 
nicates by  a  membranous  tube  with  the  oesophagus,  stomach,  or 
upper  portion  of  the  intestine. 

The  large  elongated  liver  is  of  a  soft  texture,  light  colour,  and 
divided  into  many  lobes,  it  is  provided  with  arterial  and  portal  cir- 
culation, and  generally  with  a  large  gall-bladder  as  in  other  pre- 
daceous  vertebrata.  Several  long  hepatic  ducts  join  the  cystic,  and 
many  short  ones  run  at  once  into  the  fundus  of  the  gall-bladder, 
and  the  short  but  wide  choledochus  either  opens  separately  or  in 
common  with  one  or  more  of  the  pancreatic  ducts  into  the  upper 
portion  of  the  intestine.  The  spleen  is  small,  of  various  forms, 
attached  to  the  side  of  the  stomach,  generally  simple,  but  lobulated 
in  the  shark  and  sturgeon,  as  in  some  of  the  cetacea,  and  in  the 
lamprey,  which  has  neither  pancreas  nor  gall-bladder,  it  is  wholly 
absent,  as  in  the  invertebrata.  The  pancreas  which  is  wanting  in 
the  centriscus,  presents  every  stage  of  development,  from  one  or 
two  simple  follicles  as  in  the  lophius,  choetodon,  (fee,  up  to  a  large, 
compact,  reniform  mass,  enveloped  in  a  muscular  tunic,  as  in  the 
sturgeon  and  xiphas.  The  large  pancreatic  follicles  are  connected 
by  loose  cellular  tissue,  and  admit  the  digested  food  info  their  in- 
terior, like  the  biliary  tubes  of  some  mollusca.  The  peritoneum 
lines  the  walls  of  the  abdomen,  and  surrounds  the  viscera  in  the  same 


VERTEBRATA.  71 

manner  as  in  snails,  and  the  sepias:  it  form  a  small  mesentery  and 
a  rudimentary  epiploon,  and  it  presents  the  remarkable  peculiarity 
of  its  cavity  communicating  with  the  surrounding  medium  by  the 
tvyo  small  openings,  placed  at  the  side  of  the  anus. 

AMPHIBIA. 

These  animals,  like  the  fishes,  are  predaceous  in  their  habits, 
and  swallow  their  food  without  mastication.  The  whole  of  them 
have  prehensile  teeth  in  the  palate ;  salamanders  have  them  in  both 
jaws,  frogs  in  the  upper  only,  and  the  toad  and  pipa  in  neither,  but 
in  the  toad  two  small  transverse  rows  exist  behind  the  posterior 
nares.  The  teeth  in  the  proteus  nearly  resemble  those  of  the  sala- 
mander, but  in  the  siren  they  are  arranged  in  a  quincunx  order  as 
in  many  fishes,  and  amount  nearly  to  two  hundred.  The  salivary 
glands  are  absent  in  the  aquatic,  and  merely  rudimentary  in  the 
terrestrial  amphibia.  In  the  toad  and  perennibranchiate  amphibia 
the  tongue  is  short,  thick,  and  fleshy,  but  in  the  frog  it  is 
long,  free,  bifid,  covered  with  papillae  and  mucous  follicles,  as  in 
reptiles  The  short,  dilatable,  fleshy  oesophagus,  leads  to  a  narrow, 
transversely  elongated  stomach,  muscular  in  it  parietes,  and  over- 
lapped by  a  large  bilobate  liver  with  a  distinct  gall  bladder.  In 
the  young  tadpole  of  the  frog  the  almentary  canal  is  very  long,  the 
intestine  which  is  narrow  and  coiled,  measures  ten  times  the  length 
of  the  space  from  the  mouth  to  the  anus,  but  after  the  metamorphosis 
has  occurred,  and  that  the  mixed  food  of  the  tadpole  is  changed  for 
that  of  a  more  nutritious  nature,  as  snails,  worms,  ccc,  the  canal 
becomes  gradualy  shortened  to  one  fourth  of  its  former  length.  The 
duodenum  has  transverse  folds  like  valvular  conniventes,  and  the 
short,  wide  colon  ends  in  the  cloaca,  together  with  the  openings  of 
the  genital  and  urinary  organs.  The  mucous  membrane  forms 
longitudinal  folds  in  the  proteus,  the  triton,  the  pipa,  and  the  sala- 
mander;  transverse  folds  in  the  froo-,  and  quadrangular  cells  in 
the  hyla.  A  small  pyloric  valve  exists  in  the  toad  and  pipa,  and 
the  valve  of  the  colon  is  distinct  in  the  frog,  the  triton,  and  the 
hyla.  The  liver,  the  spleen,  and  the  pancreas  are  found  in  all  the 
amphibia,  varying  in  shape  according  to  the  form  of  the  animal. 
Thus  we  perceive  in  the  lower  orders  of  amphibia,  an  evident 
approach  in  their  digestive  organs  to  those  in  fishes,  in  the  great 
number  of  teeth,  shortness  and  width  of  oesophagus,  absence  of 
fundus  to  the  stomach,  want  of  distinction  between  large  and  small 
intestine,  and  the  magnitude  of  the  liver.  But  in  many  we  discover 
an  approximation  to  the  higher  vertebrata,  in  having  fewer  teeth, 
an  elongated  tongue,  fundus  to  the  gastric  cavity,  distinction  between 
large  and  small  intestine,  absence  of  pyloric  and  colic  valves,  and 
the  development  of  transverse  folds  in  the  duodenum. 


72  EVERS's  COMPARATIVE  ANATOMY. 


REPTILIA. 


The  ophidian  and  saurian  reptiles  chiefly  subsist  on  animal  food, 
therefore  their  digestive  apparatus  will  be  found  to  differ  from  that 
of  the  chelonia  which  live  on  vegetable  substances.  The  teeth  of 
serpents  are  sharp,  conical,  inverted,  unopposed,  and  set  in  loose, 
movable  bones,  adapted  for  seizing  and  lacerating  their  prey,  they 
are  attached  to  the  maxillary,  inter-maxillary,  sphenoid,  and  palate 
bones,  and  the  poison  fangs  of  the  venomous  species  are  perforated 
and  grooved  in  front  to  transmit,  the  secretion  of  the  poison  gland 
forced  out  by  muscular  pressure.  The  tongue  is  long,  smooth, 
sheathed,  and  bifurcated.  The  salivary  glands  vary  in  the  differ- 
ent species;  the  sublingual  is  always  present,  and  the  poison  gland, 
which  is  analogous  to  the  parrotid,  is  confined  to  the  noxious  spe- 
cies, and  is  placed  below  and  behind  each  orbit.  The  long,  disten- 
sible oesophagus,  copiously  supplied  with  mucus,  leads  to  the  long, 
straight,  capacious  stomach,  longitudinally  plicated  and  capable  of 
being  distended  to  many  times  the  size  of  the  body ;  it  tapers  to  the 
pyloric  orifice,  which  is  provided  with  a  distinct  valve,  and  embraced 
by  sphinctorial  fibres.  The  duodenum  presents  a  villious  surface, 
and  receives  the  pancreatic  and  biliary  ducts;  the  remainder  of  the 
small  intestine  is  narrow  and  convoluted  to  the  commencement  of 
the  short,  dilated  colon,  where  there  is  generally  a  circular  valve 
and  a  small  coecum.  The  colon  ends  in  the  cloaca  together  with 
the  ureters,  oviducts,  or  vasa  deferentia,  and  the  male  organ  of 
generation,  single  or  divided,  also  passes  through  the  cloaca,  as  in 
other  oviparous  vertebrata.  The  liver,  spleen,  pancreas,  the  kid- 
neys, the  testes,  and  the  ovaria  present  an  elongated  form  conform- 
able to  the  shape  of  the  body.  The  small  intestines  are  attached 
to  a  mesentery,  and  the  large  are  often  sacculated  for  the  purpose 
of  retarding  the  passage  of  the  food. 

As  most  of  the  sauria  are  carnivorous  like  the  ophidia,  they  pre- 
sent a  form  of  alimentary  apparatus  equally  simple.  Their  prehen- 
sile teeth  are  fewer  and  chiefly  restricted  to  the  jaws;  the  stomach 
is  short  and  round  in  the  form  of  a  gizzard,  with  a  pair  of  central 
tendons ;  the  small  intestine  is  long  in  the  phytophagous  species 
as  the  scincus  and  iguana,  and  in  all  other  respects  they  resemble 
the  ophidian  reptiles. 

The  phytophagous  chelonia  present  a  higher  development  of 
alimentary  canal  than  the  carnivorous  species.  The  place  of  teeth 
is  supplied  by  the  sharp  horny  margins  of  the  jaws ;  the  tongue  is 
covered  with  long  papilla?;  and  the  salivary  glands  are  variously 
developed  in  the  different  species.  The  long,  wide,  muscular  oeso- 
phagus leads  to  a  large  fleshy  stomach,  extended  transversely,  and 
without  a  pyloric  valve.  The  intestine  is  about  six  times  the  length 
of  the  body,  and  the  colon  presents  a  short,  wide  coecum,  and  a 
circular  valve  at  its  commencement  in  the  terrestrial,  but  not  in  the 
aquatic  species.     The  alimentary  canal  is  wide  and  muscular,  and 


VERTEBRATA.  73 

the  mucous  membrane  folded  longitudinally  so  as  to  form  a  surface 
of  considerable  extent.  The  rectum  dilates  into  a  cloaca  which 
receives  the  openings  of  the  urinary  and  genital  organs. 

AVES. 

Nothing  can  be  more  beautiful  to  observe  than  the  rigid  economy 
which  is  displayed  in  the  accurate  adaptation  of  the  digestive 
apparatus  of  birds  to  the  various  and  dissimilar  kinds  of  iood  on 
which,  from  their  diversified  living  habits  they  are  destined  to  subsist. 
The  absence  of  teeth  in  this  class  is  supplied  by  strong  horny 
beaks  and  powerful  muscular  gizzards,  the  former  performing  the 
part  of  cutting,  and  the  latter  of  grinding  teeth  ;  the  form  of  the 
bill  will  vary  according  to  the  food  of  the  different  species  of  birds 
and  their  mode  of  procuring  it,  thus  in  the  climbing  frugivorous 
maccaws,  parrots,  and  cockatoos,  it  is  broad  and  powerful  to  break 
the  hard  shelly  coverings  of  seeds,  and  most  of  the  granivorous 
order  have  a  similar  structure.  The  broad  bills  of  ducks,  geese, 
and  other  aquatic  species  are  well  adapted  for  obtaining  worms  and 
other  substances  from  watery  or  muddy  situations,  whilst  the  eagle, 
the  hawk,  the  owl,  and  other  rapacious  birds  have  short,  strong, 
arched,  dense  bills,  with  cutting  edges,  equally  suited  to  seize,  cut, 
or  tear  their  living  prey.  The  tongue,  which  in  birds  serves  the 
purpose  of  a  prehensile  organ,  is  as  variable  in  form  as  the  bills, 
being  long,  broad,  and  covered  with  recurved  spines  in  the  swans; 
short,  round,  and  flexible  in  the  parrots  and  cockatoos,  and  short 
and  muscular  in  the  struthious  birds.  The  tongue  of  the  flamingo 
is  very  remarkable,  it  is  composed  of  an  elastic,  cellulo-fatty  sub- 
stance, its  form  is  nearly  cylindrical,  the  pointed  apex  being  sup- 
ported by  an  osseous  plate  iuferiorly.  A  deep  groove  runs  along 
the  centre  of  the  upper  surface  with  a  row  of  recurved  spines  on 
either  side.  The  os  hyoides  in  this  class  very  much  resembles  that 
of  reptiles,  and  the  length  of  its  glosso-hyal  element  chiefly  deter- 
mines the  length  of  the  tongue. 

Since  the  food  for  birds  remains  but  a  short  time  in  the  mouth 
and  undergoes  very  little  change  there,  their  salivary  glands  are 
small.  In  the  crow  they  consist  of  a  series  of  conical  follicles 
situated  along  the  sides  of  the  mouth,  and  opening  separately  on 
its  mucous  surface;  in  most  other  birds,  however,  there  are  four 
pairs,  one  under  the  tongue,  another  at  the  junction  of  the  angles 
of  the  lower  jaw,  another  close  to  the  cornua  of  the  os  hyoides,  and 
the  fourth  is  placed  at  the  angles  of  the  mouth:  they  are  most 
developed  in  the  frugivorous  species.  The  uvula  and  velum  are 
not  present,  and  the  narrow  laryngeal  aperture  is  protected  by  the 
retroverted  papillae  at  the  base  of  the  tongue,  except  in  the  coot,  the 
albatross,  and  a  few  others  where  the  epiglottis  exists  merely  in  a 
rudimentary  form  quite  insufficient  to  cover  the  opening. 

There  is  a  remarkable  pouch  under  the  jaw  of  the  pelican  which 
serves  as  a  net  for  seizing  fish,  and  is  capable  of  containing  ten 


74 


VE  ANATOMY. 


quarts  of  water;  a  similar  provision  is  found  in  the  swift,  the  rook, 
the  male  bustard  at  maturity,  and  other  insectivorous  birds.  The 
alimentary  canal  is  much  longer  and  more  capacious,  and  the  glan- 
dular apparatus  better  developed  in  the  phytophagous  birds  than 
in  those  which  subsist  more  exclusively  on  animal  food.  The  long, 
wide,  fleshy  oesophagus,  with  a  cuticular  lining-,  passes  down 
behind  and  to  the  right  side  of  the  trachea,  behind  the  heart 
and  between  the  lungs.  In  rapacious  birds  it  is  capable  of  enor- 
mous dilatation,  but  in  the  flamingo  its  diameter  does  not  exceed 
half  an  inch.  In  the  frugivorous,  insectivorous,  and  omnivorous 
birds,  the  oesophagus  presents  nearly  a  uniform  capacity  all  through, 
but  in  the  raptorial  eagles  and  vultures,  which  gorge  themselves  at 
uncertain  periods,  it  forms  a  lateral  dilatation  at  the  lower  part  of 
the  neck  termed  the  ingluvies  or  crop.  And  in  those  birds  which 
live  exclusively  on,  and  require  to  take  a  large  quantity  of  vegetable 
food,  the  crop  is  large,  globular  or  oval,  single  in  the  common  fowl, 
and  double  in  the  pigeon  ;  it  is  altogether  wanting  in  the  swan  and 
goose.  The  oesophagus  and  crop  are  supplied  with  an  abundant 
mucous  secretion,  and  are  provided  with  an  external  circular  and 
an  internal  longitudinal  set  of  muscular  fibres,  the  reverse  of  the 
disposition  observed  in  the  human  subject.  Mr.  Hunter  has  re- 
corded in  his  animal  economy,  some  interesting  observations  on 
the  crop  of  the  pigeon,  from  which  it  appears  that  this  macerating 
paunch  takes  on  a  secreting  function  during  the  breeding  season, 
and  supplies  the  young  pigeons  with  an  abundance  of  milk,  a  diet 
suitable  to  their  tender  a^e,  and  the  analogy  of  the  pigeon's  milk  to 
that  of  the  mammalia  has  not  escaped  popular  notice. 

That  part  of  the  oesophagus  which  extends  from  the  crop  to  the 
gizzard,  was  called  by  Mr.  Hunter  the  lower  oesophagus ;  at  its  in- 
ferior part,  just  above  the  gizzard,  it  dilates  into  the  glandular  divi- 
sion of  the  stomach,  variously  termed  the  jjroventriculus,  ventri- 
cular succenturiatus,  bulbus  glandulosus,  echinus,  infundibulum. 
In  the  omnivorous  and  piscivorous  tribes  there  is  no  perceptible 
dilatation  here,  but  in  all  it  presents  increased  vascularity  as  it  is 
provided  with  a  number  of  glands  which  secrete  a  fluid  analogous 
to  the  gastric  juice.  Beneath  the  infunbulum  is  the  powerful 
muscular  gizzard  directed  transversely  like  the  stomach  of  the 
vertebrita,  overlapped  by  the  lobes  of  the  liver,  and  lined  internally 
with  a  thick,  dense  epithelium.  At  the  upper  part  of  the  gizzard 
are  two  openings,  one  large,  to  the  left  side,  and  communicating 
with  the  proventriculus,  the  other  smaller,  and  a  little  to  the  right, 
leads  into  the  duodenum.  In  those  birds  which  feed  on  grain  and 
other  hard  substances,  the  muscular  fibres  of  the  gizzard  are  dis- 
tinguished by  their  density  and  red  colour,  they  are  arranged  in 
four  masses,  two  lateral,  called  the  digastric  muscles,  and  connected 
to  anterior  and  posterior  tendons,  and  two  smaller  ones  between 
these,  at  the  end  of  the  gizzard,  termed  musculi  intermedii.  In 
rapacious  and  carnivorous  birds  the  parietes  of  the  gizzard  are  thin 
and  membranous,  yet  distinctly  presenting  the  anterior  and  posterior 


VERTEBRATA.  75 

tendons.  The  gallinaceous  birds,  in  which  the  gizzard  is  most 
powerful,  swallow  pebbles  and  other  hard  bodies,  which  serve  the 
purpose  of  reducing  their  food,  like  the  gastric  teeth  of  crustacea, 
insects,  and  gasteropods ;  but  in  the  carnivorous  birds,  with  a  thin 
membranous  gizzard,  no  such  substances  are  required,  all  the  neces- 
sary changes  being  effected  by  the  activity  of  the  gastric  secretions. 
The  parietes  of  this  organ  are  subservient  in  a  remarkable  manner 
to  a  known  law,  to  which  the  whole  muscular  system  yields,  that 
of  increasing  its  growth  in  proportion  to  the  functions  imposed  on 
it;  this  was  strikingly  illustrated  in  the  case  of  a  sea-gull,  which 
Mr.  Hunter  kept  for  a  year,  living,  contrary  to  its  nature,  upon  grain. 
At  the  end  of  that  period  he  contrasted  its  gizzard  with  that  of 
another  sea  gull,  which  had  been  living  on  fish,  and  found  that  the 
digastric  muscles  of  the  former  had  acquired  nearly  three  times  the 
development  of  the  latter.  He  accomplished  similar  phenomena  by- 
changing  the  food  of  an  eagle  and  of  a  tame  kite,  the  former  throve 
very  well  on  bread,  but  that  it  was  dissatisfied  with  its  fare,  is  to  be 
inferred  from  its  seizing  the  earliest  opportunity  of  breaking  its 
chain,  and  effecting  its  escape.  These  facts  show  in  a  clear  manner 
the  provision  of  nature  for  the  preservation  of  life  under  a  variety 
of  circumstances. 

The  intestine  is  shorter  in  birds  than  in  mammalia,  its  different 
divisions  are  better  marked  than  in  the  lower  classes,  and  in  the  young 
bird  a  remnant  of  the  entrance  of  the  vesicula  umbilicalis  may  be 
seen  on  the  interior  part  of  the  small  intestine  in  the  form  of  a 
small  ccecal  appendage,  and  in  many  gallinaceous  and  some  aquatic 
birds  it  remains  through  life.  The  course  of  the  small  intestine 
varies  much  in  the  different  orders  of  birds;  the  duodenum  always 
makes  a  long  fold,  which  embraces  the  long,  bilobate  pancreas  in 
its  concavity.  The  large  intestine  is  about  a  tenth  part  of  the 
length  of  the  body,  and  usually  has  two  coeca  at  its  commencement, 
except  in  the  bustard  and  ostrich,  it  runs  a  straight  course  from 
the  cceca  to  the  cloaca  ;  it  is  generally  a  little  larger  than  the  small 
intestine,  and  its  villi  are  shorter,  coarser,  and  fewer.  The  coeca 
coli  are  of  great  size  in  the  gallinaceous  and  other  granivorous 
birds,  where  they  arise  by  two  narrow  canals,  and  enlarge  into 
wide  sacs,  often  several  times  the  size  of  the  intestine,  as  in  the 
turkey.  In  the  ostrich  they  have  the  mucous  membrane  disposed 
in  the  form  of  a  spiral  fold.  They  are  least  developed  in  the  gral- 
latores  and  the  nocturnal  rapacious  birds.  In  the  herons  and  several 
other  birds  there  is  but  one,  as  in  the  invertebrate  and  lower  ver- 
tebrate animals,  and  as  in  the  plantigrade  carnivora,  they  are  alto- 
gether wanting  in  the  zygodactylous  birds. 

The  rectum  terminates  by  a  round  valvular  orifice  in  a  dilatable 
cavity,  the  upper  part  of  the  cloaca,  which  is  the  remains  of  the 
allantois,  and  now  forms  a  rudimental  urinary  bladder,  and  in  the 
ostrich  it  serves  for  the  retention  of  the  urine  as  in  the  higher 
viviparous  animals.     At  the  lower  and  back  part  of  this  urinal  por- 


76  EVERs's  COMPARATIVE  ANATOMY. 

tion  of  the  cloaca  are  the  openings  of  the  ureters,  and  external  to 
these,  the  openings  of  the  oviducts,  or  vasa  deferentia. 

To  this  urethro-sexual  canal,  succeeds  the  preputial  cavity,  or 
lower  portion  of  the  cloaca,  which  lodges  the  organs  of  excitement, 
clitoris  or  penis,  as  in  reptiles,  marsupial,  and  monotrematous  mam- 
malia. In  the  median  plain,  and  on  the  dorsal  aspect  of  the  prepu- 
tial cavity  is  the  opening  of  a  conical  sac,  named  Barsa  Fibricii, 
which  lodge's  the  anal  follicles,  and  is  analogous  to  Cowper's  glands. 

The  liver  is  large  in  birds,  especially  in  the  aquatic  species,  it 
generally  consists  of  two  lobes,  but  occasionally  of  three,  as  in  the 
pigeon,  goose,  and  swan  ;  the  right  lobe  is  usually  larger  than  the 
left,  the  latter,  however,  is  larger  in  the  bustard,  where  it  extends 
into  the  pelvis.  The  bile  is  discharged  by  two  ducts,  one  goes 
directly  to  the  duodenum,  the  other  to  the  gall-bladder,  and  when 
the  latter  is  absent,  they  both  open  separately  into  the  duodenum, 
but  in  no  case  is  there  a  ductus  choledochus.  The  pancreas,  long, 
narrow,  and  trihedral,  is  lodged  in  the  fold  of  the  duodenum,  its 
ducts  are  two,  sometimes  three  in  number,  as  in  the  pigeon,  raven, 
and  common  fowl,  and  they  terminate  separately  in  the  duodenum. 
The  small,  round,  oval,  flat,  or  elongated  spleen  is  placed  beneath 
the  liver,  and  to  the  right  of  the  proventriculus;  its  texture  is  loose, 
and  the  blood  would  seem  to  be  deposited  in  cells,  from  which  the 
veins  take  it  up. 

When  we  contemplate  the  different  lengths  and  forms  of  intestine 
met  with  in  this  class,  we  cannot  help  attributing  it  to  some  wise 
purpose,  and  a  little  reflection  on  the  greatly  diversified  nature  of 
the  food  on  which  the  various  tribes  of  birds  are  destined  to  subsist, 
irresistibly  leads  us  to  infer  that  economy  seems  to  be  the  main 
design  ;  for  instance,  the  colon  and  coeca  of  the  African  ostrich, 
which  has  to  subsist  on  the  scanty  and  uncertain  fare  of  the  desert, 
are  fifty  times  the  length  of  the  same  parts  in  the  cassowary,  which 
inhabits  Java,  one  of  the  most  fertile  countries  on  the  globe. 

MAMMALIA. 

The  digestive  organs  vary  more  in  this  than  in  any  other  of  the 
vertebrated  classes,  and  the  varieties  will  be  found  to  refer  chiefly 
to  the  type  of  development  and  living  habits  of  the  sundry  species. 
The  teeth  present  infinite  varieties  as  to  form  and  position  ;  however, 
their  density  and  fixedness  are  well  calculated  to  disintegrate  ali- 
mentary substances,  and  blend  them  with  the  mucous  and  salivary 
secretions.  The  teeth  are  wanting  in  the  ant-eaters,  pangolins,  and 
the  whalebone  whale.  The  young  ornithorhynchus  paradoxus  has 
two  molar  teeth  in  each  jaw  on  each  side:  these  are  shed  in  the 
adult  animal,  and  replaced  by  one  large  one  on  each  side.  But  in 
the  hystrix  there  are  twenty  small,  blunt,  horny  teeth,  near  the  base 
of  the  tongue,  and  seven  transverse  rows  in  the  corresponding  sur- 
face of  the  palate.  The  incisor,  canine,  and  molar  teeth  exist  in 
the  quadrumana.  carnivora,  ruminantia,  without  horns,  and  in  most 


VERTEBRATA.  77 

of  the  pachydermata ;  but  it  is  only  in  the  extinct  anoplotherium 
among  mammalia,  that  the  three  kinds  of  teeth  are  arranged 
in  an  uninterrupted  series,  as  in  man.  The  superior  incisors  are 
wanting  in  the  ruminantia,  and  the  inferior  in  the  walrus.  The 
Ethiopian  hog  and  certain  bats  lose  their  incisors  at  a  particular 
age.  The  canine  teeth  are  absent  in  the  rodentia,  some  ruminants, 
and  in  most  of  the  female  solipeda.  The  rodentia  have  but  two 
incisors  in  each  jaw,  with  the  exception  of  the  hare  and  rabbit, 
which  have  them  double  in  the  upper  jaw;  the  kangaroo  has  two 
below  and  eight  above  ;  the  daman  two  above  and  four  below.  The 
molar  teeth  are  the  most  essential,  and  are  the  last  to  disappear: 
hence  the  ornithorhynchus  paradoxus,  the  tatu,  and  the  two-horned 
rhinoceros,  are  restricted  to  them.  The  molar  teeth  are  renewed 
eight  times  in  the  elephant,  the  incisors  are  shed  twice  in  many 
rodentia  ;  and  most  of  the  teeth  are  renewed  once  in  the  other 
orders  of  the  mammalia.  In  most  mammalia  which  feed  on  animal 
substances,  the  crowns  of  the  teeth  are  entirely  covered  with  enamel, 
and  only  partially  so  in  the  phytophagous  quadrupeds. 

The  following  is  an  outline  of  the  process  by  which  the  teeth 
are  produced.  About  two  months  after  conception,  a  gelatinous 
substance  lies  alonsf  each  alveolar  arch:  at 'the  third  month  this 
substance  is  firmer,  and  lodged  in  a  shallow  groove  in  the  bone.  It 
is  next  divided  into  separate  pulps  by  transverse  filaments  passing 
from  one  side  of  the  alveolous  to  the  other.  These  pulps  are  en- 
closed in,  and  connected  by  vessels  to  a  thin  vascular  membrane, 
which,  between  the  third  and  fourth  month  begins  to  secrete  the 
ossific  laminae  from  its  outer  surface.  This  membrane,  with  its 
contained  pulp,  is  supplied  from  the  dental  vessels,  and  nerves,  and 
is  surrounded  by  a  thick  vascular  sac,  separable  into  two  layers  ; 
•  he  latter  membrane  is  attached  to  the  pulp  only  at  its  base,  but  is 
firmly  connected  by  its  outer  layer  to  the  gum,  from  which  it  derives 
its  vascular  and  nervous  supplies.  It  is  from  the  inner  surface  of 
the  internal  layer  of  this  sac  that  the  enamel  is  secreted,  and  at 
this  period  it  becomes  thick  and  vascular,  whilst  the  outer  layer, 
which  is  only  rudimentary  in  man,  secretes  the  crusta  petrosa  in 
the  graminivorous  quadrupeds.  After  the  enamel  has  been  secreted, 
both  layers  of  this  sac  become  wholly  absorbed,  hence  they  have 
been  termed  the  deciduous  membranes,  in  contra-distincti<  n  to  the 
permanent,  which  are  described  as  three  in  number,  one  being  the 
periosteum  of  the  alveolus,  another  the  periosteum  of  the  root, 
and  the  third  the  periosteum  of  the  dental  cavity,  which  secreted 
the  tooth.  But  in  fact  these  three  permanent  membranes  are  simply 
a  continuation  of  the  periosteum  of  the  jaw  which  first  lines  the 
alveolus,  then  descends,  to  form  the  periosteum  of  the  root,  and 
lastly  passes  up  in  the  form  of  a  hollow  cone  to  enclose  the  pulp. 
The  period  at  which  the  teeth  appear  in  the  human  subject  is  very 
variable,  some  children  being  born  with  two  or  more,  whilst  in 
others  they  may  not  appear  for  two  or  even  three  years.  From  five 
to  eight  months,  however,  is  the  most  usual  period ;  they  generally 


78 

appear  first  in  the  lower  jaw,  and  proceed  in  the  following  order  : — 
From  5  to  8  months,  the  four  central  incisors;  from  7  to  10,  the 
lateral  incisors;  from  12  to  16,  the  four  anterior  molars ;  from  14 
to  20,  the  four  cuspidati ;  and  from  18  to  36  months,  the  four  pos- 
terior molars. 

The  purposes  of  prehension  are  accomplished  by  sensitive  fleshy 
lips,  as  in  herbivorous  quadrupeds,  by  a  long,  flexible  tongue,  as  in 
the  giraffe  and  ant-eaters,  and  by  other  organs  such  as  the  proboscis 
of  the  elephant.  The  salivary  glands  are  largest  in  herbivorous 
quadrupeds,  less  in  the  carnivora,  and  least  in  the  aquatic  mamma- 
lia. The  sublingual  glands  are  wanting  in  cats.  The  velum  palati 
is  large,  but  the  uvula  is  confined  to  the  quadrumana.  The  os 
hyoides,  is  most  developed  in  the  herbivorous  quadrupeds,  and  has 
been  shown  by  Geoffroy  to  consist  of  twelve  elements,  a  glosso  and 
basi-hyal  piece  for  the  body,  an  apo  a  cerato,  and  a  styl-hyal  ele- 
ment tor  each  of  the  anterior  corn u a,  and  an  ento  and  uro-hyal  for 
each  of  the  smaller  posterior  cornua.  This  condition  is  sometimes 
found  as  an  abnormal  state  in  man.  The  oesophagus  is  wide  and 
dilatable  in  the  carnivora,  and  narrow  and  fleshy  in  the  herbivora. 
The  arrangement  of  its  muscular  fibres  is  the  same  as  in  man  ;  and 
its  mucous  tunic,  wh'ich  usually  forms  longitudinal  and  but  rarely 
transverse  folds,  is  lined  with  cuticle,  which  in  the  carnivora  termi- 
nates at  the  cardiac  orifice  in  a  fringed  margin,  but  lines  half  the 
stomach  of  the  horse,  the  rat,  the  hog,  and  some  others  of  the  pecora, 
and  in  the  ruminantia  it  lines  the  three  first  cavities  of  the  stomach. 
The  oesophagus  of  the  ornithorynchus  hystrix  is  furnished  with  a 
peculiar  valve  at  its  commencement,  and  numerous  papillse  at  its 
termination,  directed  upwards,  and  its  cuticular  lining  is  continued 
through  the  stomach. 

The  animal  nature  of  the  food  of  the  carnivora  bespeaks  a  short 
and  simple  form  of  alimentary  canal.  In  some,  as  the  lion  and  the 
cat,  the  stomach  is  elongated  in  form,  and  its  orifices  remote  from 
each  other,  this  is  particularly  the  case  in  the  lynx;  in  others,  as 
the  racoon,  it  is  nearly  globular,  and  in  all,  with  the  exception  of 
the  seal,  its  interior  is  smooth,  and  almost  without  villi.  The 
monotremata,  cheiroptera,  insectivora,  and  marsupialia,  also  present 
a  simple  stomach,  a  coecal  portion  being  but  little  developed. 
When,  however,  the  food  is  of  a  more  mixed  character,  the  stomach 
becomes  more  elongated  transversely,  as  in  the  quadrumana  and 
others  of  the  less  carnivorous  tribes.  In  most  of  the  rodentia  the 
thin  cardiac  portion  forms  a  distinct  coecum,  and  is  separated  by  a 
constriction  from  the  pyloric  muscular  portion.  Several  of  the 
pachydermata,  marsupialia,  edentata,  and  quadrumana,  form  a  link 
of  transition  to  the  more  complex  stomachs  of  the  cetacea  and 
ruminantia  in  the  formation  of  folds  or  coeca  with  cuticular  linings. 
Thy  intestinal  canal  is  very  short  in  these  animals,  the  whole  tract 
not  exceeding  three  times  the  length  of  the  body  in  the  lion  and 
wild  cat.  In  the  badger  there  is  scarcely  any  distinction  between 
small  and  large  intestine:  but  in  the  lion,  seal,  and  others,  it  is  well 


VERTEBRATA. 


79 


marked.  The  coecum  is  small  in  cats,  spiral  in  dogs,  and  generally 
absent  with  the  colic  valve  in  the  mustelidae.  Valvulse  conniventes 
are  scarcely  developed. 

In  thecetacea  the  tongue  is  short,  thick,  fleshy,  and  but.  little  sus- 
ceptible of  motion,  and  in  the  whale  it  often  affords  three  barrels  of 
oil.  The  teeth  are  prehensile,  the  salivary  glands  rudimental  or 
deficient,  and  the  oesophagus  short  and  wide.  In  the  phytophagous 
cetaceans  the  stomach  is  divided  into  a  large  cardiac,  and  a  small 
pyloric  portion,  by  a  contraction  which  gives  origin  to  twotubiform 
prolongations.  The  coecum  is  simple  in  the  dugong,  and  bifurcated 
in  the  manatee.  In  the  zoophagous  cetacea  the  stomach  consists  of 
four  or  five  compartments,  none  of  which,  except  the  first,  have  any 
communication  with  the  oesophagus,  therefore  no  rumination  can 
occur.  The  first  cavity  is  small  and  lined  with  cuticle,  which  ter- 
minates abruptly  at  the  narrow  opening  leading  into  the  second.  A 
smal|  pyloric  orifice  leads  to  a  dilated  duodenum.  There  is  scarcely 
any  distinction  between  small  and  large  intestine,  and  the  coecum 
coli  is  but  little  developed.  Why  so  complicated  a  stomach  should 
exist  in  animals  nourished  by  the  most  digestible  and  highly  organ- 
ised food,  is  an  anomaly  for  which  we  can  offer  no  explanation,  but 
one  which,  from  its  interest,  courts  early  investigation. 

The  stomach  of  the  kangaroo  resembles  the  human  colon  and 
caecum;  the  oesophagus  enters  near  its  left  extremity,  which  is 
small  and  bifid;  the  stomach  first  extends  towards  the  right  side, 
and  then  upwards  and  to  the  left,  in  such  a  manner  as  to  completely 
encircle  the  entrance  of  the  oesophagus,  and  terminates  at  the  py- 
lorus by  a  contracted  orifice.  Its  cavity  gradually  enlarges  from  the 
left  extremity  till  it  nearly  reaches  the  pylorus,  it  then  dilates  into  a 
round  cavity  with  two  lateral  processes,  and  finally  ends  by  a 
narrow  orifice.  It  presents  a  sacculated  appearance  arising  from 
the  presence  of  anterior  and  posterior  bands  like  those  of  the  human 
colon,  and  the  cuticle  lines  it  to  a  certain  extent  on  either  side  of 
the  entrance  of  the  oesophagus.  This  animal  has  been  known  to 
ruminate  when  fed  on  hard  ifood.  The  kangaroO-rat  and  the  vam- 
pyre  bat  present  similar  modifications  of  stomach  but  have  no  part 
of  it  lined  with  cuticle,  and  in  the  former  there  is  a  valve  at  the 
cardiac  orifice.  The  intestine  of  the  kangaroo  corresponds  in  its 
great  length  and  convolutions  with  the  coarse  nature  of  its  vegetable 
food,  and  the  coecum  is  about  fifteen  inches  long.  At  the  cardiac 
orifice  of  the  stomach  in  the  beaver  and  wombat  there  is  a  large 
gastric  gland,  like  the  glandular  infundibulum  in  birds. 

The  ruminating  animals  possess  four  stomachs  ;  the  first  magnus 
venter,  or  paunch,  receives  the  crude  unrnasticated  food,  while  the 
animal  is  grazing.  When  this  cavity  is  filled  the  animal  retires  to 
rest,  and  begins  to  ruminate;  the  unmasticated  food,  softened  in 
the  paunch,  now  passes  in  small  portions  into  the  second  cavity, 
called  reticulum,  or  honey  comb ;  from  this  it  passes  as  a  bolus  up 
through  the  oesophagus  to  the  mouth,  where  it  is  thoroughly  mas- 
ticated and  insalivated  ;  it  is  next  couducted  by  the  oesophagus  to 


80  EVERS'S  COMPARATIVE  ANATOMY. 

the  third  stomach,  termed  mam/plies,  or  omasum,  aid  from  thence 
into  the  fourth  stomach  called  abo?nasum,  or  rennet  bag-.  Of  these 
cavities,  the  first  is  the  largest,  and  the  third  the  smallest.  The  three 
first  are  lined  with  cuticle,  and  the  fourth,  which  is  next  in  capacity 
to  the  paunch  is  lined  with  a  soft  mucous  coat  folded  in  the  longitu- 
dinal direction.  This  is  the  proper  digestive  stomach,  and  is  analo- 
gous to  the  digestive  sac  of  carnivorous  and  higher  quadrupeds. 
The  fourth  stomach  of  the  ruminantia  is  the  first  developed  ;  in  the 
earlier  periods  of  life  it  is  the  largest,  and  the  only  one  employed  in 
digestion.  The  mechanism  by  which  milk  is  transmitted  directly 
into  the  fourth  stomach  during  the  period  of  suckling  is  this,  the 
G3Sophagus  enters  just  where  the  three  first  cavities  approach  each 
other,  here  it  can  open  directly  into  the  first  or  second  stomach,  but 
instead  of  terminating  there,  it  is  continued  in  the  form  of  a  groove 
with  prominent  lips,  which  admit  of  being  drawn  together  so  as  to 
form  a  complete  canal,  which  then  constitutes  a  direct  continuation 
of  the  oesophagus  into  the  third  stomach,  but  this  cavity  not  having 
been  distended  with  solid  food  in  the  young  animal,  it  merely  forms 
a  tube  through  which  the  milk  passes  into  the  fourth  stomach.  In 
the  adult  animal  the  same  mechanism  continues,  but  here  the  third 
cavity  having  been  already  distended,  receives  the  bolus  after 
rumination. 

In  the  ruminants  without  horns,  as  the  dromedary,  the  camel, 
and  the  lama,  a  somewhat  different  but  not  less  beautiful  mechanism 
prevails,  fitting  them  to  live  in  the  sandy  deserts  and  arid  plains 
they  inhabit.  In  these  animals  the  paunch  consists  of  two  com- 
partments, the  first  of  which  receives  the  un masticated  food  from 
which  it  is  returned  to  the  mouth,  moistened  by  the  fluid  of  the 
second  or  cellular  compartment.  After  the  cud  has  been  chewed, 
the  food  passes  along  the  upper  part  of  the  second  cavity  into  the 
third,  and  from  that  to  the  fourth.  When  the  camel  drinks,  the 
water  passes  directly  into  the  second  cavity,  and  when  this  is  full 
it  flows  into  the  neighbouring  cellular  compartment  of  the  paunch. 
In  the  bullock,  the  three  first  cavities  are  lined  with  cuticle ;  in  the 
camel  it  lines  only  the  two  first,  and  terminates  just  within  the  ori- 
fice of  the  third,  the  surface  of  which  has  a  faint  appearance  of 
honey-comb  structure.  From  the  comparative  view  which  has 
been  taken  of  the  stomach  of  the  bullock  and  camel,  it  appears,  that 
in  the  bullock  there  are  three  cavities  formed  for  the  preparation  of 
of  the  food,  and  one  for  its  digestion.  In  the  camel,  the  two  com- 
partments of  the  first  cavity  answer  the  purposes  of  the  two  first 
stomachs  of  the  bullock  ;  the  second  is  employed  as  a  reservoir  for 
water  only  ;  the  third  is  so  small  and  simple  in  its  structure,  that  it 
is  not  easy  to  ascertain  its  particular  office,  whilst  the  fourth  is  that 
in  which  the  process  of  digestion  is  accomplished. 

As  a  general  rule,  it  may  be  stated  that  the  intestinal  canal  is 
long,  large,  and  sacculated  in  the  herbivorous  tribes,  and  short, 
straight,  and  without  sacculi,  in  the  carnivora.  Some  remarkable 
exceptions,  however,  present  themselves,  for  instance  in  makies, 


VERTEBRATA.  81 

mice,  and  shrews  which  are  purely  frugivorous,  and  in  sloths, 
which  live  on  vegetable  food,  the  intestine  measures  only  about 
three  times  the  length  of  the  body;  whilst  in  the  porpoise  and  seal, 
which  live  on  animal  food,  it  measures  in  the  former  11  times,  and 
in  the  latter  28  times  the  length  of  the  body.  But  this  apparent 
anomaly  is  explained  by  recollecting  that  the  caecum  plays  a  com- 
pensating part  with  respect  to  the  other  portions  of  the  alimentary 
canal,  indeed  the  researches  of  the  Heidelberg  professors  authorise 
us  in  believing  that  it  acts  the  part  of  a  second  stomach,  and  that 
where  the  latter  is  simple,  the  coecum  presents  a  complex  and 
highly  developed  condition,  and  vice  versa.  Hence  by  a  reference 
to  the  highly  developed  coecnm  and  vermiform  appendix  of  the 
rodentia,  we  are  enabled  to  reconcile  their  simple  form  of  stomach 
with  their  herbivorous  food.  In  the  elephant,  the  small  intestine 
measures  3S  feet,  the  colon  and  rectum  20£  feet,  and  the  coecum  1£. 
In  the  camel,  the  small  intestine  is  71  feet,  the  colon  and  rectum 
56,  and  the  coecnm  3.  The  intestine  is  10  times  the  length  of  the 
body  in  the  horse,  and  28  times  in  the  sheep.  In  an  ornitho- 
rhynchus  17£  inches  long,  the  small  intestine  measured  4  feet  4 
inches,  and  the  colon  and  rectum  1  foot  4  inches.  In  this  animal, 
the  rectum,  urinary,  and  genital  organs  terminate  in  a  cloaca,  as  in 
birds  and  amphibia. 

The  solidungulous  pachydermata  masticate  their  food  before  it  is 
swallowed,  therefore  they  do  not  ruminate,  and  require  but  a  simple 
digestive  stomach  ;  but  they  have  the  same  narrow  lengthened  form 
of  intestine,  and  a  capacious  sacculated  coecum  and  colon.  The 
liver  is  largest  in  the  cetacea  and  those  animals  that  dive  or  burrow  ; 
smaller  in  the  herbivora,  and  least  in  the  carnivorous  tribes.  There 
seems  to  be  no  general  law  for  the  presence  or  absence  of  the  gall- 
bladder in  mammalia  more  than  in  birds  and  fishes  ;  it  is  for  the 
most  part  wanting  in  the  herbivorous  species,  as  the  deer  and 
the  camel  ;  it  is  also  absent  from  most  of  the  rodentia  and  pachy- 
dermata ;  and  here  the  hepatic  duct  is  generally  much  dilated,  as  in 
the  horse  and  elephant.  In  the  otter  a  similar  dilation  exists  in 
conjunction  with  a  gall-bladder.  It  is  remarkable  that  all  the 
mammalia  which  want  this  reservoir,  except  the  porpoise,  are 
phytophagous. 

In  the  course  of  my  dissections  during  my  pupilage  at  the  college, 
I,  together  with  my  esteemed  friend,  Surgeon  Bewley,  of  Moate,  met 
with  a  female  subject  about  nine  years  of  age,  in  which  this  recep- 
tacle was  absent.  I  invited  the  attention  of  Dr.  Houston  to  this,  I 
believe,  unique  anomaly,  who  has  prepared  and  deposited  the 
biliary  apparatus  in  the  museum  of  the  college. 

The  spleen  is  long,  flat,  and  attached  to  the  paunch  in  the  rumi- 
nantia,  narrow  and  lengthened  in  the  carnivora,  and  in  the  porpoise 
it  consists  of  several  portions.  The  pancreas  is  long,  flat,  and 
attached  to  the  right  end  of  the  first  stomach  in  the  cetacea,  in  other 
mammalia  it  is  longer,  and  often  divided  into  several  portions,  its 
8 — g  evers  6 


82 

duct,  which  is  double  in  the  elephant,  usually  opens  separately  into 
the  duodenum. 


RECAPITULATION. 

1.  A  digestive  cavity  is  the  most  universal  organ  in  animals,  and 
exists  in  all,  with  the  exception  of  some  of  the  monads. 

2.  Masticating,  salivary,  and  biliary  organs  are  found  in  the 
higher  radiata. 

3.  All  these  parts  are  more  highly  developed  in  the  articulata, 
and  one  or  two  gall-bladders  are  present. 

4.  There  has  been  no  gall-bladder  found  in  the  mollusca. 

5.  The  stomach  receives  the  biliary  and  pancreatic  fluids  in  all 
the  invertebrata. 

6.  The  invertebrated  animals  possess  no  portal  circulation. 

7.  In  the  vertebrate  the  alimentary  canal  always  swells  out  into 
a  gastric  enlargement.  The  tributary  organs  are  large  and  conglo- 
merate, and  the  salivary  glands  are  rarely  absent. 

8.  The  duodenum  receives  the  biliary  and  pancreatic  secretions, 
and  there  are  no  teeth  found  in  the  stomach. 

9.  As  a  general  rule  the  alimentary  canal  is  larger  and  longer  in 
the  vegetable-eating  animals,  than  in  those  that  live  on  flesh. 

10.  Fishes  have  a  simple  form  of  alimentary  canal,  their  teeth  are 
often  numerous,  as  in  the  pike,  rarely  absent  as  in  the  sturgeon, 
their  salivary  glands  are  rudimental,  or  entirely  wanting,  and  their 
whole  canal  often  measures  but  half  the  length  of  the  body. 

11.  The  digestive  apparatus  undergoes  interesting  changes  during 
the  metamorphosis  of  the  frog,  &c. 

12.  The  teeth  are  absent  in  birds,  and  their  place  supplied  by  bill 
and  gizzard. 

13.  The  crop  is  double  in  the  pigeon,  single  in  the  fowl,  and 
absent  from  the  goose.  The  gizzard  is  thick  and  powerful  in  the 
granivorous,  but  thin  and  membranous  in  the  carnivorous  species, 
and  the  great  intestine  terminates  in  the  dilatable  rectal  vestibule 
which  receives  the  openings  of  the  ureters,  of  the  oviducts,  or  vasa 
deferentia,  and  of  the  Bursa  Fabricii. 

14.  The  teeth  are  greatly  modified  in  the  mammalia,  being 
rarely  absent,  as  in  the  man  is  or  pangolin,  the  myrmecophaga  and 
the  echidna. 

15.  The  digestive  system  is  most  complex  in  the  herbivorous 
ruminantia,  and  most  simple  in  the  carnivora  ;  in  the  latter  the 
food  requires  but  little  elaboration,  hence  the  form  of  the  teeth,  and 
the  great  strength  of  the  jaws  are  admirably  adapted  for  seizing  and 
tearing  their  living  prey,  here  also  we  have  a  simple  stomach,  and 
a  short  intestine,  without  any  provision  to  retard  its  contents.  In 
the  ruminantia,  on  the  contrary,  the  jaws  are  elongated,  and  admit 
of  free  lateral  motion  with  flat  grinding  teeth,  the  stomach  is  com- 
plicated, and  the  intestine  long  and  sacculated  ;  in  fact  all  things 


ABSORBENT  SYSTEM.  83 

conspire  to  ensure  perfect  comminution  of  the  food,  retardation  of 
its  passage,  and  a  due  absorption  of  its  nutritious  particles. 


CHAPTER  XII. 

ABSORBENT  SYSTEM. 

Although  Monro,  Poli,  Sheldon,  and  Carus,  have  described  chy- 
liferous  vessels  in  many  of  the  invertebrated  classes,  their  existence 
in  these  animals  has  not  yet  been  satisfactorily  proved,  and  it  is  more 
than  probable  that  their  function  is  performed  by  the  veins,  the  white 
blood  of  which  resembles  the  chyliferous  fluid  of  the  vertebrata. 
The  chyle  varies  much  in  its  composition  and  properties  in  the 
various  tribes  of  vertebrated  animals,  and  even  in  the  same  animal 
according  to  the  sort  of  food  it  lives  on,  being  of  a  pinkish  tint,  with 
abundance  of  crassamentum  in  the  different  animals  which  subsist 
on  nutritious  animal  food,  while  it  is  limpid  and  pale,  with  a  great 
proportion  of  serum  in  the  inferior  animals.  The  chyliferous,  like 
the  other  systems  of  the  body,  presents  different  grades  of  develop- 
ment in  the  different  vertebrated  classes.  Thus,  in  fishes  the 
vessels  seem  to  consist  of  a  single  tunic,  destitute  of  valves,  and 
without  conglobate  glands  ;  they  form  two  strata  of  vessels  between 
the  coats  of  the  intestine,  and  carry  a  limpid  fluid  to  the  recepta- 
culum  chyli,  from  which  one  or  two  thoracic  ducts  lead  to  the 
jugular  veins  or  other  branches  of  the  cavee.  The  lymphatics  and 
lacteals  communicate  frequently  with  one  another,  and  with  the 
neighbouring  veins,  and  when  injected  they  present  a  beaded  ap- 
pearance owing  to  the  presence  of  rudimentary  valves. 

The  chyliferous  system  in  the  amphibia  is  the  same  as  in  fish, 
but  in  the  reptilia  it  presents  a  higher  degree  of  formation  in  the 
existence  of  valves,  and  the  milkish  appearance  of  the  chyle,  the 
place  of  glands  is  still  supplied  by  the  convoluted  condition  of  the 
vessels  as  in  fishes  ;  here  also,  two  or  more  thoracic  ducts,  fre- 
quently communicating,  pass  to  the  jugular  or  subclavian  veins,  or 
the  angle  between  them,  previously  receiving  the  lymphatics  from 
the  head,  neck,  and  arms.  In  the  tortoise,  the  anastomoses  of  the 
thoracic  ducts  nearly  conceal  the  trunk  of  the  aorta.  This  system 
presents  a  somewhat  higher  grade  of  development  in  birds,  both 
sets  cf  vessels  being  more  numerous  and  distinct,  the  valves  are 
more  abundant,  but  yet  admit  of  the  passage  of  fluids  from  trunks 
to  branches.  Glands  appear  now  for  the  first  time,  in  connection 
with  the  lymphatics,  but  not  with  the  lacteals.  Two  thoracic  ducts, 
having  but  few  anastomoses,  terminate  by  several  openings  at  the 
junction  of  the  jugular  and  subclavian  veins. 

In  the  mammalia  the  absorbent  system  is  better  developed  and 


84  EVERS'S  COMPARATIVE  ANATOMY. 

mora  distinct  from  the  sanguiferous  than  in  any  of  the  preceding 
classes,  as  manifested  in  the  sanguineous  characters  of  the  chyle, 
the  elaborate  structure  of  the  vessels,  the  perfect  condition  of  their 
valves,  the  increased  number  of  conglobate  glands,  and  the  unity 
and  distinctness  of  the  thoracic  duct.  Sometimes  this  duct  is 
double,  as  in  the  dog,  and  sometimes  its  branches  open  into  the  vena 
azygos,  as  in  the  hog.  Occasionally  its  trunk  divides,  and  having 
enclosed  a  narrow  elongated  space,  called  insula  Halleri,  the 
branches  again  unite.  The  mesenteric  glands  are  of  great  magni- 
tude in  the  cetacea,  more  detached  in  the  pachydermata,  and  grouped 
into  a  mass,  named  pancreas  Assellii,  in  the  carnivora. 

RECAPITULATION. 

1.  Lymphatics  have  been  described,  but  not  saticfactorily  demon- 
strated, in  the  invertebrata. 

2.  No  conglobate  glands  have  been  found  in  fishes  ;  their  absorb- 
ents are  thin,  convoluted,  and  furnished  with  rudimentary  valves, 
and  occasionally  two  thoracic  ducts  exist. 

3.  This  system  is  the  same  in  amphibia  as  in  fishes,  but  in  the 
reptilia  the  valves  are  more  perfect. 

4.  In  birds  the  absorbents  are  very  numerous,  the  valves  still 
more  perfect,  and  glands  for  the  first  time  met  with. 

5.  In  mammalia  the  entire  system  is  marked  by  a  higher  type  of 
formation  :  the  thoracic  duct  is  sometimes  double  as  in  the  dog, 
and  occasionally  opens  into  the  vena  azygos  as  in  the  hog. 


CHAPTER  XIII. 

SANGUIFEROUS  SYSTEM   IN  THE  INVERTEBRATA. 

The  systemic,  or  red-blood  circulation  was  discovered  in  the 
higher  animals  by  Harvey,  in  1619;  and  by  the  researches  of 
modern  comparative  anatomists,  it  has  been  found  to  have  a  much 
more  extended  existence  ;  there  is  a  considerable  number,  however, 
of  the  cycloneurose  classes  of  animals,  in  which  no  distinct  vascular 
system  has  as  yet  been  detected.  The  first  appearance  of  it  which 
we  observe  in  the  lower  animals,  as  in  the  earliest  condition  of  the 
human  embryo,  consists  of  vessels  alone,  through  which  the  fluids 
move  in  a  circle,  like  the  colourless  blood  in  the  cells  of  a  plant. 
In  the  asterias,  echinus,  and  holothuria  among  the  echinodermata, 
a  large  vessel,  in  the  form  of  a  ring,  surrounds  the  commencement 
of  the  alimentary  canal,  from  which  the  systemic  arteries  are 
derived  ;  the  systemic  veins  send  branches  to  the  gills,  from  which 
the  blood  is  returned  by  one  large  vessel  to  the  heart. 


SANGUIFEROUS  SYSTEM  IN  THE  INVERTEBRATA.  85 

Diplo-neura. — In  the  earth-worm  two  vessels,  one  above  and  the 
other  below,  extend  the  entire  length  of  the  body;  they  communi- 
cate by  several  cross  branches,  and  join  at  their  extremities,  where 
small  dilatations  are  observable,  supposed  to  aid  in  propelling  the 
blood,  which  moves  in  opposite  directions.  The  large  vessels  of  the 
annelida  are  endowed  with  a  contractile  power,  and  in  insects, 
spiders,  and  the  lower  species  of  Crustacea,  large  dilatations  occur, 
capable  of  considerable  contractility. 

In  the  leech,  hirudo  vulgaris,  the  two  principal  vessels  are  placed 
on  the  sides,  and  lesser  ones  above  and  below,  all  anastomosing 
freely  by  transverse  branches  ;  of  these  the  superior  longitudinal 
and  the  inferior  transverse  only  pulsate.  It  is  the  opinion  of 
Miiller  that  the  lateral  vessels  alternately  empty  themselves  from 
behind  forwards  ;  and  others  state  that  the  blood  is  moved  forwards 
in  the  upper  vessel  and  backwards  in  the  lower. 

The  arachnidans,  which  breathe  by  means  of  trachae,  seem  to  have 
a  dorsal  vessel  only,  without  any  ramifications.  Those,  on  the 
contrary,  which  possess  branchial  lungs,  have  a  well  developed  cir- 
culatory apparatus.  The  blood  leaving  the  heart  by  the  arteries  is 
distributed  to  all  parts  of  the  body ;  having  become  venous  it  is 
returned  to  the  pulmonary  branchiae  by  sinuses  which  supply  the 
place  of  veins,  and  having  undergone  arterialisation,  it  is  returned 
to  the  heart  by  the  branchio-cardiac  vessels,  again  to  be  propelled 
through  the  arteries. 

In  the  higher  Crustacea  the  heart  consists  of  two  sinuses  and  a 
ventricle  ;  from  the  latter,  in  the  stomopoda,  six  vessels  arise  which 
distribute  the  blood  to  the  eyes,  liver,  antennas,  (fee.  This  fluid 
is  next  returned  to  venous  sinuses  in  the  neighbourhood  of  the 
branchiae,  through  passages  without  any  apparent  parietes ;  the 
arterialised  blood  is  brought  from  the  branchiae  to  the  sinuses  of  the 
heart  by  vessels  named  branchio-cardiacs,  from  which  it  is  received 
by  the  ventricle  and  sent  into  the  arteries  issuing  from  it,  each  of 
which  is  provided  with  a  valve  at  its  origin. 

Cyclo-gangliata. — The  greater  number  of  the  animals  which 
compose  this  class  are  aquatic,  and  enjoy  a  branchial  respiration. 
In  the  ascidiae  the  heart  is  very  simple,  consisting  merely  of  a  thin 
membranous  ventricle  destitute  of  valves.  The  conchifera  have 
two  auricles  and  a  ventricle;  the  gasteropoda  and pteropoda possess 
a  strong  auricle  and  ventricle  provided  with  valves.  In  the  cepha- 
lopoda there  is  an  aortic  heart,  and  two  branchial  hearts,  or  dilata- 
tions ;  in  these  animals,  the  blood  having  been  carried  to  the  system 
by  the  arteries  is  returned  by  the  veins  to  the  branchial  fringes ;  in 
some  bivalves,  however,  a  portion  of  it  is  sent  direct  to  the  heart 
without  passing  through  the  respiratory  organ.  In  the  gastero- 
podous  and  other  mollusca  the  rectum  passes  through  the  ventricle. 


86  EVERS'S  COMPARATIVE  ANATOMY. 

CHAPTER  XIV. 

SANGUIFEROUS  SYSTEM  IN  THE  VERTEBRATA. 

In  the  greater  number  of  the  invertebrate  animals  which  we  have 
hitherto  examined,  the  heart  and  principal  artery  were  placed  above 
the  alimentary  canal  and  the  chief  part  of  the  nervous  system  ;  but 
in  the  vertebrate  classes  the  converse  order  obtains,  the  heart 
being  below  the  alimentary  tract;  in  the  former  division  the  blood 
generally  arrives  at  the  heart  after  having  passed  through  the  re- 
spiratory organ,  while  in  the  latter  the  blood  flows  from  the  heart 
to  the  respiratory  organ.  In  the  invertebrate  classes,  too,  there  is 
no  vena  porta,  the  liver  being  supplied  by  an  hepatic  artery  alone. 

PISCES. 

The  gills,  which  are  the  only  respiratory  organs  of  fishes,  are 
placed  in  the  course  of  the  arterial  circulation.  The  venous  blood 
from  all  parts  of  the  body  is  conducted  to  a  single  auricle  which 
propels  it  into  the  ventricle,  from  which  it  is  brought  by  the 
arterial  bulb  to  the  gills,  where  it  is  arterialised,  and  from  which  it 
is  distributed  by  the  branches  of  the  aorta  to  all  parts  of  the  body. 
The  caudal  vein  of  the  eel  presents  a  contractile  dilatation,  to  which 
Dr.  Hall  has  applied  the  name  of  caudal  heart;  this  doubtless 
assists  in  promoting  the  circulation  in  the  caudal  branches  of  the 
vena  cava.  Many  look  upon  the  heart  of  fishes  and  the  artery 
issuing  from  it  as  analogous  to  the  right  heart  and  pulmonary 
artery  of  higher  animals  ;  but  it  is  much  more  just  to  consider  the 
heart  as  corresponding  to  the  whole  heart  of  the  warm-blooded 
vertebrata,  seeing  that  in  some  of  the  reptiles  possessing  gills,  the 
blood  is  sent  to  these  organs  through  the  great  systemic  trunk.  In 
fact,  the  heart,  in  these  animals,  acts  at  once  the  part  of  a  pulmo- 
nary and  a  systemic  heart  in  propelling  the  blood  not  only  to  the 
gills,  but  through  all  parts  of  the  aortic  system. 

Portal-circulation. — The  porta  in  fishes  carries  to  the  liver  the 
venous  blood  from  the  stomach,  intestines,  spleen,  pancreas,  and 
occasionally  from  the  genital  organs,  swimming  bladder,  and  tail. 
In  the  gadus,  however,  as  in  reptiles,  the  venous  blood  from  the  tail 
and  the  central  parts  of  the  abdomen  goes  to  the  kidneys.  In  the 
silurus  the  blood  from  the  posterior  part  of  the  body  is  distributed 
to  the  liver  and  kidneys :  and  in  the  carp,  pike  and  perch,  to  these 
organs  and  to  the  vena  cava.  This  vessel  also  receives  the  blood 
from  the  testicle,  ovary,  kidneys,  and  frequently  from  the  swimming 
bladder. 

AMPHIBIA. 

The  metamorphosis  which  this  class  of  animals  undergoes  in 
passing   from  the  pisciform  to  the  reptilian  state,   is  strikingly 


SANGUIFEROUS  SYSTEM  IN  THE  VERTEBRATA.  87 

illustrated  in  their  circulatory  system  :  beginning  life  with  the 
single  heart  of  a  fish,  and  ending  it  with  the  double  heart  of  a 
reptile.  In  the  water  salamanders  the  venous  blood  which  has  cir- 
culated through  the  body,  is  returned  to  a  systemic  auricle,  and 
having  passed  through  the  ventricle,  it  is  received  by  the  bulbus 
arteriosus,  and  sent  by  the  branchial  arteries  to  the  branchial 
leaflets.  The  pure  blood  is  now  received  by  the  pulmonary  veins, 
the  confluence  of  which  constitute,  as  in  fishes,  the  descending 
aorta. 

From  this  latter  vessel  a  small  branch  passes  off  to  the  rudiment- 
ary lung,  which  is  afterwards  to  become  the  pulmonary  artery.  As 
the  animal  changes  from  an  aquatic  to  an  atmospheric  respiration, 
the  branchiag  become  absorbed,  and  the  lungs  proportionally  deve- 
loped. Their  arteries  experience  corresponding  changes,  those  of 
the  former  organs  diminishing,  while  those  of  the  latter  increase 
with  the  growth  of  the  lung.  The  two  veins  which  return  the 
blood  from  the  rudimental  lung  also  enlarge,  and  as  they  arrive  at 
the  heart,  they  undergo  a  remarkable  dilatation,  which  constitutes 
the  left  auricle.  Till  lately  the  bi-auricular  form  of  heart  was  sup- 
posed to  be  confined  to  the  caducibranchiate  amphibia,  as  frogs, 
toads,  salamanders,  and  tritons,  but  the  researches  of  Owen  have 
proved  its  existence  in  the  perennibranchiate  amphibia  also. 

At  the  same  time  that  the  systemic  auricle  receives  the  impure 
blood  from  the  cavae,  the  pulmonic  auricle  receives  the  aerated 
blood  from  the  lungs.  From  both  of  these  cavities  the  blood  is  sent 
into,  and  mixed  in,  the  single  ventricle,  from  which  it  is  sent  by 
the  one  impulse  to  the  lungs  and  to  the  system  generally.  From 
this  description  it  is  obvious  that  the  blood  is  but  partially  purified, 
mixed  blood  being  sent  through  the  pulmonary  arteries,  as  well  as 
through  the  aorta  and  its  ramifications. 


REPTILIA. 

In  this  class  of  animals  we  perceive  a  still  higher  grade  of  deve- 
lopment than  was  met  with  in  the  amphibia;  the  ventricle  is  par- 
tially divided  by  a  septum  into  two  compartments,  corresponding 
in  most  particulars  to  the  two  ventricles  of  warm-blooded  animals. 
In  some  the  septum  is  so  imperfect  as  to  be  incapable  of  preventing 
the  admixture  of  the  blood  derived  from  both  auricles.  In  others, 
however,  as  the  crocodile,  the  ventricles  are  separated  completely, 
or  communicate  by  a  small  orifice  provided  with  a  valve,  which 
prevents  the  blood  passing  from  one  compartment  to  the  other.  In 
fact  the  heart  in  this  singular  animal  is  double,  as  in  the  higher 
vertebrata,  so  that  the  venous  blood  returned  by  the  cava?  to  the 
right  auricle,  passes  from  the  right  ventricle  through  the  pulmonary 
artery  to  the  lungs,  while  the  pure  blood  returned  from  this  organ 
to  the  left  auricle  is  directed  from  the  left  ventricular  compartment 
through  the  systemic  arteries.  The  auriculo-ventricular  orifices  are 
provided  with  a  muscular  valve,  and  in  the  crocodile  there  are  two. 


88 

It  is  curious,  however,  that  in  the  whole  of  this  class  the  descending 
aorta  is  formed  by  the  union  of  two  branches,  the  right  branch 
arises  from  the  left  ventricular  compartment,  consequently  carries 
pure,  or  nearly  pure  blood,  which  it  distributes  to  the  head,  neck, 
chest,  and  upper  extremities.  The  left  branch,  on  the  contrary, 
arises  either  from  the  right  ventricular  compartment,  or  what  is 
tantamount  to  it,  from  the  pulmonary  artery.  It  is  obvious,  then, 
that  the  descending  aorta  carries  a  mixed  quality  of  blood  to  the 
parts  it  supplies;  but  it  is  interesting  to  observe,  that  previous  to 
the  junction  of  the  two  aortic  arches,  the  left  gives  off  the  cosliac 
axis  which  supplies  the  entire  alimentary  canal  and  digestive  organs 
with  venous  blood.  In  the  turtle,  lizard,  and  some  serpents,  where 
the  septum  ventriculorum  is  imperfect,  the  pulmonary  artery  and 
aorta  at  once  carry  mixed  blood,  and  in  some  of  the  chelonia, 
as  the  tortoise,  the  existence  of  ductus  arteriosus  ensures  a  more 
complete  mixture  of  venous  and  arterial  blood.  The  arteries  arising 
from  the  ventricles  are  each  provided  wtth  two  valves. 

Portal  system. — In  amphibia  and  reptiles,  as  in  fishes,  there 
are  two  lesser  venous  circulations;  the  one  belongs  to  the  liver, 
and  the  other,  which  does  not  exist  in  birds  or  mammals,  belongs 
to  the  kidneys.  In  some  reptiles  ail  the  venous  blood  from  the 
posterior  parts  of  the  body  is  distributed  to  the  liver  and  kidneys, 
while  in  others  a  portion  is  sent  to  the  inferior  cava ;  this  latter 
vessel  also  receives  the  venous  blood  which  has  circulated  through 
the  kidneys. 


AVES. 

The  heart,  in  this  highly  organised  class  of  oviparous  animals 
consists  of  four  separate  and  distinct  compartments,  and  indeed  pre- 
sents a  more  perfect  typical  form  than  is  met  with  in  even  the  mam- 
malia. Its  form  is  conical,  being  sometimes  short  and  wide,  as  in 
the  crane,  and  sometimes  more  elongated,  as  in  the  emeu.  Its 
situation  is  mesial,  its  axis  parallel  to  that  of  the  trunk,  and  in  con- 
sequence of  the  partial  development  of  the  diaphragm  its  apex  rests 
between  the  lobes  of  the  liver.  The  right  auricle  seems  consider- 
ably larger  than  the  left,  and  the  auricular  portion  is  distinctly 
divided  from  the  sinus  by  two  semilunar  muscular  valves;  one 
attached  along  the  anterior,  and  the  other  along  the  posterior  side 
of  the  sinus.  The  venous  blood  is  returned  to  the  sinus  of  the 
auricle  by  an  inferior  and  two  superior  venas  cavae,  and  it  is  re- 
markable that  the  left  superior  cava  receives  the  coronary  vein  just 
before  its  termination.  The  orifice  of  this  vessel  is  opposite  to  that 
of  the  inferior  cava,  but  separated  from  it  by  a  semilunar  mem- 
branous valve.  The  auriculo-ventricular  opening  is  a  small  oblique 
slit,  and  reflux  from  the  ventricle  is  prevented  by  a  thick  strong 
muscular  valve  so  disposed  as  to  give  considerable  impulse  to  the 
flow  of  blood  through  the  pulmonary  artery.  There  is  a  small 
muscular  column  at  the  upper  part  of  the  orifice,  but  it  is  only  one 


SANGUIFEROUS    SYSTEM  IN  THE  VERTEBRATA.  89 

of  the  carnese  columnse,  of  which  few  exist  in  the  ventricle.  In 
the  left  auricle  a  mere  rudiment  of  valve  is  found  between  the  sinus 
and  the  appendix.  The  parietes  of  the  left  ventricle  are  very  thick, 
and  the  auriculo-ventricular  opening1  is  guarded  by  two  mem- 
branous folds  corresponding  to  the  mitral  valve  in  mammalia.  The 
pulmonary  artery  and  aorta  are  provided  at  their  origins  with  three 
semilunar  valves,  those  of  the  former  vessel  being  thicker  and 
stronger  than  those  of  the  latter.  The  extremities  of  these  valves 
will  be  found  by  careful  dissection  to  be  attached  to  cartilaginous 
or  osseous  points  imbedded  in  the  fibrous  tunic  of  the  vessels. 

The  pulmonary  artery  having  arisen  from  the  right  ventricle  at 
once  divides  into  two  branches,  one  for  each  lung;  from  these  or- 
gans the  blood  is  returned  by  two  veins,  which  unite  before  they 
reach  the  left  auricle.  From  the  left  ventricle  arises  the  aorta, 
which  immediately  sends  off  two  branches  analogous  to  arteriae 
innominatae,  for  the  supply  of  the  head  and  wings.  It  may  be 
observed  that  birds  possess  no  palmar  arches,  nor,  strictly  speaking, 
a  radial  artery.  The  cerebral,  orbital,  temporal,  and  spermatic 
arteries  are  remarkable  for  their  free  and  plexiform  anastomoses. 
But  of  all  the  arterial  plexuses,  that  of  the  organ  of  incubation 
requires  special  notice.  It  is  formed  by  branches  from  the  posterior 
thoracic,  abdominal,  cutaneous,  and  ischiadic  arteries,  immediately 
under  the  integuments  of  the  abdomen.  This  plexus  becomes 
enormously  enlarged  during  the  period  of  incubation. 

The  venous  system  in  birds  is  remarkable  for  the  frequency  of 
its  communications,  especially  one  which  exists  between  the  united 
caudal,  hemorrhoidal,  and  iliac  veins  and  the  vena  porta,  by  means 
of  which  the  blood  from  the  viscera  and  posterior  parts  of  the  body 
may  flow  either  into  the  cava  or  porta,  a  disposition  obviously  de- 
signed to  guard  against  congestions:  as  yet  it  is  a  question  con- 
cerning which  contradictory  opinions  prevail,  as  to  whether  the 
branches  of  the  pulmonary  artery  extend  to  the  air-cells  distributed 
over  the  body,  or  whether  the  blood  in  the  systemic  capillaries  un- 
undergoes  any  change  tending  to  its  purification  in  the  parietes  of 
these  cells. 


MAMMALIA. 

The  form  of  the  heart,  and  the  distribution  of  the  blood  vessels  in 
the  whole  of  this  class  so  closely  resemble  the  human  type,  that  it 
becomes  necessary  to  notice  only  a  kw  individual  peculiarities  ;  in 
the  dugong  and  rytina  for  instance,  among  the  cetacea,  the  heart  is 
cloven  by  the  deep  separation  of  its  two  ventricles,  and  the  orifice 
of  the  inferior  cava  is  guarded  by  a  fleshy  Eustachian  valve,  which 
is  wholly  absent  in  the  lion,  the  bear,  and  the  dog.  In  the  mono- 
tremata,  the  marsupiata,  the  porcupine,  and  the  elephant,  the  right 
auricle  receives  one  inferior  and  two  superior  cavae  as  in  birds,  and 
the  coronary  vein  terminates  in  the  left  superior  cava.  In  the 
ourang-outang  and  the  mole,  only,  is  the  apex  of  the  heart  inclined 


90  EVERS's  COMPARATIVE  ANATOMY. 

to  the  left  side  as  in  the  human  subject.  In  the  upper  part  of  the 
substance  of  the  left  ventricle  of  the  pig,  the  stag",  and  other  bisulea, 
are  two  small  flat  bones,  cruciformly  disposed  in  the  stag,  they  are 
formed  about  the  third  year  of  the  animal's  life,  and  are  but  slightly 
developed  in  the  female.  It  has  been  generally  supposed  that  the 
foramen  ovale  and  ductus  arteriosus  remain  permanently  open  in 
seals,  otters,  and  cetaceans,  and  although  the  dissections  of  Cuvier, 
Home,  Blumenbach,  and  T.  Bell,  go  to  prove  that  they  have 
remained  unclosed  in  a  few  instances,  still  we  must  look  upon  these 
as  exceptions,  admitting,  however,  that  these  passages  continue 
longer  pervious  in  these  diving  animals  than  in  other  mammalia. 

As  regards  the  arterial  system  some  remarkable  peculiarities  are 
observed  in  the  branches  arising  from  the  arch  of  the  aor^a,  thus 
in  the  horse,  the  camel,  and  many  of  the  long  necked  mammalia, 
this  great  trunk  just  after  its  origin  divides  into  two  branches,  one 
becomes  the  descending  aorta,  the  other  ascends  vertically  and 
divides  into  a  right  innominata,  a  left  subclavian  and  a  left  carotid, 
which  latter  appears  in  direction  the  continuation  of  the  trunk.  In 
the  elephant  there  is  but  one  coronary  artery,  and  both  carotids 
arise  by  a  common  trunk  between  the  two  subclavians. 

The  dolphin  has  an  innominata  on  each  side,  this  constitutes  the 
type  of  the  cheiroptera.  In  the  marmot  and  the  guinea-pig,  the 
right  innominata  gives  rise  to  the  two  carotids,  and  the  right  sub- 
clavian. This  also  is  the  type  of  the  order  quadrumana,  and  most 
of  the  carnivora.  Among  the  peculiarities  in  the  distribution  of 
arteries  we  may  notice  the  rete  mirabile  formed  by  the  internal 
carotid  at  its  entrance  into  the  cranium  in  several  carnivora  and 
ruminant  bisulca ;  the  plexifonn  arrangement  of  arteries  which 
exists  under  the  pleurae  and  between  the  ribs  in  the  cetacea  ;  and 
the  remarkable  anastomosing  divisions  of  the  arteries  of  the  extre- 
mities and  tail  in  the  slow  moving  and  climbing  animals  as  the 
bradypus,  myrmecophaga,  pangolin,  and  stenops.  This  condition 
of  the  arterial  system  doubtless  has  reference  to  the  peculiar  living 
habits  of  the  animal  it  exists  in,  thus  in  the  cetaceans  these  serpen- 
tine vessels  constitute  so  many  reservoirs  for  containing  arterial 
blood  during  the  obstructions  to  the  circulation  which  are  almost 
inseparably  connected  with  the  aquatic  habits  of  these  mammalia, 
whilst  in  those  with  depending  heads,  the  rete  mirabile  is  admirably 
calculated  to .  obviate  the  injurious  effects  of  sudden  influxes 
to  the  brain,  and  in  the  edentata  the  arterial  divisions  alluded 
to  are  no  less  indicated,  lest  the  large  trunks  of  the  extremities 
should  suffer  from  pressure  during  their  long  continued  action 
in  climbing. 

The  plexiform  disposition,  which  characterises  so  many  parts  of 
the  arterial  system,  is  no  less  strikingly  displayed  in  the  venous. 
This  is  well  seen  in  the  tortuous  sinuses  which  receive  the  inter- 
costal veins  in  the  porpoise,  the  vena  azygos  being  absent  in  this 
animal.  A  beautiful  distribution  of  veins  constituting  the  rete 
mirabile  venosum,  is  met  with  on  the  foot  of  the  horse,  where  these 


SANGUIFEROUS  SYSTEM  IN  THE  VERTEBRATE.  91 

vessels  run  in  innumerable  parallel  branches  on  the  anterior  surface 
of  the  coffin  bone.  Another  peculiarity  in  this  system  is  presented 
by  the  inferior  cava,  in  the  porpoise,  the  seal,  the  common  and  the 
sea  otter,  consisting  in  a  considerable  dilatation  of  this  vessel 
between  the  liver  and  the  diaphragm,  similar  to  what  is  observed 
in  tortoises  and  diving  birds. 

A  general  review  of  the  vascular  system  indicates  that  the  heart 
in  its  simplest  form  resembles  a  vessel  endowed  with  contractility, 
as  exemplified  by  the  vessel-like  multiple  hearts  which  constitute 
the  vascular  trunks  of  the  annelides,  the  contractile  trunks  on  the 
alimentary  canal  of  the  holofhuria,  the  dorsal  vessel  of  insects,  &c. 
In  the  embryo  of  the  highest  warm-blooded  animals  the  heart  is  at 
first  tubular,  and  it  is  interesting  to  observe,  that  during  the  progress 
of  its  development  it  passes  through,  and  resembles  the  several  forms 
which  constitute  its  permanent  type  in  the  adult  state  of  fishes  and 
reptiles,  even  the  clefts  in  the  neck,  with  the  arched  divisions  of  the 
aortic  trunk,  which  are  persistent  in  reptiles,  may  be  seen  in  the 
human  embryo  at  a  very  early  stage  of  its  development,  and  the 
ductus  arteriosus,  which  is  single  in  mammalia,  but  double  in  birds, 
is  the  last  of  those  arches  which  remains  unclosed  in  the  foetus. 
These  arches  may  be  well  seen  by  inspecting  the  embryo  of  a  bird 
on  the  third  day  of  incubation. 

The  frequency  of  the  heart's  action  varies  much  in  different  ani- 
mals, and  even  in  the  human  subject,  from  a  variety  of  causes. 
In  a  fish  it  beats  in  a  minute  from    20  to  24 
In  the  frog,  about        -        -  60 

In  birds,  from  -        -  100—140 

In  the  bat,  -        -  200 

In  rabbits,  -  120 

In  the  cat,  -  J 10 

In  the  dog,  -         -  95 

In  the  sheep,  -  75 

And  the  horse,  -  40 

In  the  human  embryo,  -  150 

At  birth,  -        -         130  to  140 

During  the  first  year    -        -         115 — 130 
During  the  second  year        -  100 —  115 

During  the  third  year,  -  90 —  100 

During  the  seventh  year,      -  85 —   90 

About  the  fourteenth  year    -  80 —   85 

in  the  middle  period  of  life,  -  70  —   75 

In  old  age,  -        -  50—65 

RECAPITULATION. 

1.  The  systemic  circulation  was  discovered  by  Harvey  in  1619. 

2.  In  the  higher  radiata  a  large  artery  surrounds  the  beginning 
of  the  alimentary  canal,  in  the  form  of  a  ring,  from  which  the 
systemic  branches  arise. 


92 


EVERSS  COMPARATIVE  ANATOMY. 


3.  A  distinct  heart  is  first  seen  in  the  Crustacea. 

4.  In  the  gasteropodous  mollusca,  as  the  snail,  the  rectum  passes 
through  the  heart. 

5.  There  is  no  portal  circulation  in  the  avertebrata. 

6.  The  heart  of  a  fish  consists  of  a  single  auricle  and  ventricle, 
and  the  blood  of  the  porta  is  distributed  to  the  liver  and  kidneys. 

7.  All  the  amphibia  have  at  first  the  single  heart  of  a  fish,  but 
the  caducibranchiate  species  terminate  life  with  the  double  heart  of 
a  reptile. 

8.  The  heart  of  birds  consists  of  four  distinct  compartments,  as 
in  mammalia,  but  rather  more  perfect,  owing  to  the  existence  of  its 
fleshy  valves. 

9.  The  heart  of  the  higher  warm-blooded  mammalia,  even  that 
of  man,  in  the  course  of  its  development,  represents  the  several 
grades  which  constitute  the  permanent  types  of  the  lower  animals. 


CHAPTER  XV. 

RESPIRATORY  SYSTEM  IN  THE  INVERTEBRATA. 

The  respiratory  organs  are  sometimes  placed  in  the  interior  of 
the  body  in  the  form  of  lungs  sometimes  towards  its  exterior  in  the 
form  of  lamellated,  ramified,  pectinated,  tufted,  ciliated,  or  pin- 
nated processes,  termed  gills,  or  branchiae,  and  a  third  form  of  re- 
spiratory apparatus  is  obtained  by  the  development  of  a  system  of 
tracheal  tubes,  ramified  to  an  exquisite  degree  of  minuteness,  and 
widely  spread  through  all  the  organs  of  the  body.  Animals  pro- 
vided with  lungs  generally  breathe  atmospheric  air,  whilst  in  those 
furnished  with  branchiae  respiration  is  accomplished  by  means  of 
water.  An  exception  to  the  former,  however,  is  met  with  in  the  holo- 
thuria;  and  to  the  latter,  in  the  terrestial  Crustacea.  It  will  appear 
in  the  progress  of  this  article  that  some  of  the  vertebrated  animals 
commence  life  by  a  branchial  respiratory  and  terminate  it  by  a  pul- 
monary, and  that  others  enjoy  a  mixed  form  of  respiratory  organ  all 
through.  In  fact,  nature  seems  almost  to  have  exhausted  her 
ingenuity  in  the  construction  and  development  of  respiratory 
apparatus. 

Cyclo-neura. — In  the  lowest  classes  of  this  division  the  only 
respiratory  organs  detectible  are  small  cilia  pervading  the  entire 
surface,  but  so  minute  as  to  require  high  magnifying  powers  to 
render  them  visible.  The  tentacula  and  the  whole  surface  of  the 
body  are  subservient  to  the  function  of  respiration  in  the  polypifera. 
In  the  asterias  and  sea-urchin  among  the  echinodermata,  the  water 
passes  into  and  out  of  the  cavity  lined  by  peritoneum,  in  which  the 
viscera  are  lodged.     In  the  holothuria  the  water  is  alternately  re- 


RESPIRATORY  SYSTEM   IN  THE  INVERTEBRATA.  93 

ceived  and  emitted  from  a  tube  which  is  ramified  in  an  arborescent 
manner,  with  terminal  cellules. 

Diplo-neura. — The  highly  vascular  skin  of  the  entozoa  performs 
the  function  of  respiration — in  some,  through  the  medium  of  water  ; 
and  in  others  the  blood  is  oxygenated  on  the  mucous  surface  of  the 
animals  they  infest.  In  the  cirrhopoda  respiration  is  performed  by 
the  arms  and  by  the  leaf-like  fringed  membranes  attached  to  the 
anterior  part  of  the  sides  of  the  body.  The  surface  of  the  body  is 
in  general  the  seat  of  respiration  among  the  annelida,  but  in  the 
lumbrici,  nereides,  and  hirudines  respiration  is  in  part  effected  by  a 
series  of  minute  membranous  sacs  under  the  skin  of  the  abdomen, 
each  having  a  separate  external  opening.  Respiration  is  aerial  in 
the  greater  number  of  insects,  the  air  being  received  through  a 
number  of  stigmata,  and  carried  by  the  tracheae  in  some  cases  into 
vesicles,  and  in  others  into  longitudinally  ramifying  trunks. 

Many  insects  in  their  larval  state  breathe  by  means  of  branchiae 
in  the  water,  and  some  in  their  perfect  condition  breathe  water, 
although  they  have  an  internal  tracheal  apparatus  ;  from  the  water 
in  these  branchiae  the  air  is  separated,  and  passed  in  the  gaseous 
state  through  the  ramified  tracheae.  There  is  a  very  curious  fact 
connected  with  the  eristalis,  this  disgusting  insect  has  the  last  ring 
of  its  body  elongated  into  a  membranous  tube,  within  which  there 
is  a  second  horny  tube,  which  the  animal  can  extend  to  the  surface 
for  the  purpose  of  respiration,  whilst  it  lives  at  the  bottom  where  it 
procures  its  food  in  the  filth  of  sloughs,  sewers,  and  stinking  privies. 
The  tracheary  aracknida  resemble  insects  in  their  tracheal  tubular 
respiration,  whilst  the  respiratory  organs  of  the  pulmonary  arachnida 
consist  of  small  sacs  opening  externally,  and  situated  at  the  under 
surface  of  the  abdomen.  Both  sets  of  organs  are  enjoyed  by  the 
segestria  and  dysdera.  In  tracing  the  progress  of  development  of 
the  respiratory  apparatus  in  the  higher  Crustacea,  as  the  astacus 
fluviatilis,  it  will  be  found  to  present  four  principal  periods  ;  lstly, 
that  which  precedes  the  appearance  of  this  apparatus  ;  2dly,  that  in 
which  the  branchiae  are  not  distinguishable  from  the  organs  dedi- 
cated to  locomotion  or  mastication  ;  3dly,  that  characterised  by  the 
transformation  of  these  into  organs  wholly  dedicated  to  respiration, 
and  distinct  from  the  extremities  ;  and  4thly,  that  during  which  the 
branchiae  sink  inwards,  and  become  lodged  in  the  branchial  cavities. 

By  reviewing  the  respiratory  apparatus  in  the  different  groups  of 
crustaceans,  it  will  be  found  that  the  several  stages  of  development 
of  the  higher  orders  constitute  the  permanent  types  of  the  lower 
series ;  thus,  to  the  first  stage  of  organisation  belong  the  greater 
number  of  the  entomostraca  and  copepoda ;  to  the  second,  the  bran- 
chiopoda  ;  to  the  third,  the  amphipoda  ;  and  to  the  fourth  the  entire 
order  of  the  decapoda.  The  greater  number  of  the  Crustacea  live 
under  water;  some,  however,  as  the  gecarcini,  or  land-crabs,  con- 
stantly live  out  of  water,  but  it  is  necessary  t!  at  their  ^piratory 
membrane  shall  be  kept  humid,  and  for  this  purpose  the  membrane 
is  thrown  into  folds  in  the  form  of  reservoirs  for  containing  water. 


94  EVERS's  COMPARATIVE  ANATOMY. 

Gyclo-gangliata. — The  greater  number  of  this  division  breathe  in 
water,  by  means  of  gills,  some  however,  breathe  by  lungs  in  the  air. 
The  first  mode  of  respiration  is  enjoyed  by  the  tunicata,  conchifera, 
pteropoda,  cephalopoda,  and  some  of  the  gasteropoda,  the  remainder 
of  this  class  breathe  atmospheric  air,  by  means  of  a  lung  in  the  form 
of  a  large  cavity,  placed  beneath  the  mantle.  A  curious  circumstance 
connected  with  the  conchifera  is,  that  the  eggs  on  escaping  from  the 
ovary,  are  deposited  between  two  layers  of  the  branchial  membrane, 
where  they  increase  in  size  and  undergo  incubation. 


CHAPTER  XVI. 

ORGANS  OP  RESPIRATION  IN  THE  VERTEBRATA. 
PISCES. 

This  entire  class  is  covered  with  branchiae,  by  means  of  which 
they  abstract  the  free  oxygen  contained  in  the  water.  In  the  sharks 
and  rays,  and  in  all  the  osseous  fishes  there  are  four  gills  on  each 
side,  supported  by  as  many  branchial  arches  of  cartilage  or  bone, 
connected  to  the  os  hyoides. 

Each  gill  consists  of  a  double  series  of  lance-shaped  lammellae 
closed  in  by  a  movable  cover,  operculum.  Generally  there  is  but 
a  single  opening  for  the  passage  of  the  water,  but  in  some 
instances,  especially  among  the  cartilaginous  fishes,  there  are 
several.  In  consequence  of  the  swimming  bladder  of  fish  being 
supposed  by  Cams,  Blumenbach,  and  many  others,  to  be  subservient 
to  the  purposes  of  respiration,  it  merits  some  notice  in  this  place. 

This  organ,  which  is  sometimes  divided  by  a  septum,  as  in  the 
genus  cyprinus,  and  sometimes  absent,  as  in  the  pleuronectes, 
Jophius,  and  mackerel,  is  placed  in  the  abdomen,  close  to  the  spine, 
and  below  the  kidney ;  consists  of  an  internal  vascular  lining 
membrane,  a  strong  fibrous  tunic,  and  a  partial  investment  of  peri- 
toneum. In  fresh-water  fishes,  it  has  been  found  to  contain  nitrogen, 
and  in  salt  water  fishes,  chiefly  carbonic  acid  gas.  From  its 
anterior  part  a  canal,  ductus  pneumaticus,  passes  forwards  and 
opens  into  the  oesophagus,  except  in  the  sturgeon  where  it 
opens  into  the  stomach.  This  duct  is  double  in  the  cod,  in  the 
carp  it  possesses  valves  so  disposed  as  to  admit  of  the  egress,  but 
prevent  the  ingress  of  air;  it  is  absent  in  the  sciura,  cobitis,  burbot, 
and  others.  When  we  consider  that  this  organ  is  largest  in  such 
fishes  as  swim  with  greatest  velocity,  and  wanting  in  those  where 
large  fins  or  a  powerful  tail  compensate  for  its  absence,  we  are  dis- 
posed to  agree  with  those  who  regard  it  as  an  organ  of  progressive 
motion. 


ORGANS  OF  RESPIRATION  IN  THE  VERTEBRATA.  95 


AMPHIBIA. 


Progs  and  salamanders  in  their  tadpole  state,  breathe  by  gills, 
which  during  the  earliest  periods  of  their  existence  are  placed  ex- 
ternally; they  also  possess  rudimentary  lungs,  which  become  deve- 
loped as  the  animals  change  from  the  aquatic  to  the  aerial  respira- 
tion. The  perennibranchiate  amphibia,  as  the  proteus,  siren,  and 
axolotl  also  possess  both  sets  of  organs,  and  retain  them  through 
life,  but  here  the  lungs  always  present  the  rudimentary  type,  and 
it  is  even  doubted  whether  they  subserve  at  all  to  the  function  of 
respiration.  In  these  as  well  as  in  the  larval  condition  of  the 
caducibranchiate  genera,  the  pulmonary  organ  is  in  the  form  of  a 
mere  sac,  and  it  is  only  during  the  metamorphosis  that  it  assumes 
the  cellular  character.  In  the  adult  state  of  all  the  higher  orders 
of  amphibia  respiration  is  accomplished  in  a  manner  different  from 
all  other  air-breathing  animals,  viz.,  the  mouth  being  fully  distended 
by  the  air  which  enters  through  the  nostrils,  these  passages  together 
with  the  pharyngo-oesophageal  are  closed,  the  mouth  then  suddenly 
contracts  by  the  action  of  the  surrounding  muscles,  and  the  air  is 
forced  by  an  effort  of  deglutition  through  the  glottis  and  trachea 
into  the  lungs.  Hence,  one  of  the  most  effectual  ways  of  killing  a 
frog  is  to  keep  its  mouth  open  for  a  short  period ;  this  mode  of 
inspiration  is  accounted  for  by  recollecting  that  the  ribs  are 
absent  in  these  animals. 


REPTILIA. 

In  most  of  the  amphibia  the  trachea  is  very  short  and  perfectly 
membranous.  In  this  class  it  is  somewhat  longer,  and  cartilaginous 
plates  begin  to  appear  in  it ;  these  plates  which  are  first  seen  in  the 
dactylethra,  do  not  form  perfect  rings,  but  present  the  appearance 
of  perforated  lamellse  irregularly  disposed.  In  the  bronchi  of  the 
casciliae,  however,  the  cartilaginous  rings  are  much  more  complete. 
In  lizards  and  serpents  the  lung  is  a  mere  cavity  with  cellular 
parietes,  having  perforations  which  communicate  with  the  neigh- 
bouring cells.  Turtles  have  a  more  complicated  structure,  approach- 
ing that  of  warm-blooded  animals. 


AVES. 

The  lungs,  in  this  class,  are  confined  to  the  back  parts  of  the 
cavities  of  the  thorax  and  abdomen  by  the  serous  membrane  com- 
mon to  these  cavities  ;  they  are  of  a  flattened,  elongated  form,  smooth 
anteriorly,  and  grooved  posteriorly  by  the  ribs,  between  which  they 
are  impacted  ;  they  are  of  a  bright  red  colour,  and  of  a  loose  spongy 
texture;  on  the  surface  of  the  lungs  there  are  openings  through 
which  air  passes  from  the  bronchial  tubes  into  large  neighbouring 
cells.     In  birds  not  organised  for  flight  these  cells,  are  confined  to 


96  EVERS'S  COMPARATIVE  ANATOMY. 

the  abdomen,  but  in  others  they  extend  along  the  neck,  and  even 
into  the  extremities:  they  also  penetrate  the  cavities  and  diploe  of 
the  bones,  a  discovery  for  which  we  are  indebted  to  Mr.  Hunter. 
This  great  physiologist  injected  the  medullary  cavities  of  the  bones 
from  the  trachea:  he  also  tied  this  tube,  and  having  broken  the 
humerus  of  a  fowl,  and  the  femur  of  a  hawk,  he  found  that  the 
birds  respired  for  a  short  time  through  the  artificial  openings.  The 
proportion  in  which  the  osseous  system  of  birds  is  permeated  by 
air  has  reference  to  their  respective  modes  of  progression,  thus 
almost  every  bone  in  the  body  admits  air  in  the  kite,  the  hawk,  the 
eagle,  and  other  birds  of  high  flight;  and  in  the  hornbill  even  the 
phalanges  of  the  toes  contain  air.  Four  uses  have  been  ascribed 
to  this  extension  of  the  respiratory  system  in  birds — first,  to  sub- 
serve the  function  of  respiration ;  secondly,  to  aid  by  mechanical 
pressure  the  action  of  the  lungs;  thirdly,  to  render  the  body  spe- 
cifically lighter  for  the  purposes  of  flight :  and  fourthly,  by  the  dis- 
tension of  the  cells  in  the  extremities  to  assist  in  maintaining  the 
wings  in  a  state  of  extension,  during  long-continued  flight.  Mr. 
Hunter  supposed  it  contributed  to  sustain  the  song  of  birds  and  to 
give  it  strength  and  tone. 

The  air  passages  in  birds  consist  of  a  superior  larynx,  a  trachea, 
and  inferior  larynx,  and  two  bronchi  with  their  ramifications.  The 
superior  larynx  is  situated  behind  the  root  of  the  tongue,  resting 
on  the  uro-hyal  element  of  the  os  hyoides ;  it  is  composed  of  from 
four  to  ten  bony  or  cartilaginous  pieces,  and  two  pairs  of  muscles ; 
thyro-arytenoidea  and  constrictores  glottidis.  The  trachea  is  com- 
posed of  a  series  of  bony  or  cartilaginous  rings,  which  form  com- 
plete circles,  with  the  exception  of  the  two  first ;  they  are  closely 
approximated,  and  sometimes  overlap.  Many  birds,  as  the  rasores, 
have  no  inferior  larynx ;  in  others  it  presents  different  degrees  of 
development,  thus,  in  the  genus  falco  there  is  but  one  pair  of 
muscles;  in  the  parrot  tribe  three,  and  in  the  insessores,  where  this 
organ  attains  its  greatest  decree  of  perfection,  five.  The  rings  of 
the  bronchi  do  not  form  complete  circles,  but  gradually  become 
smaller,  and  finally  disappear. 

MAMMALIA. 

In  the  entire  of  this  class  there  is  great  similarity  in  the  respira- 
tory organs,  not  only  to  each  other  but  to  the  human  type  of  for- 
mation. An  epiglottis  exists  in  all,  and  is  divided  at  its  superior 
extremity  in  the  seal,  the  hare,  and  the  ant-eater.  The  larynx  in 
all  the  mammalia  consists  of  the  same  parts  generally  as  in  man, 
but  occasionally  modified  in  obedience  to  particular  circumstances. 
Thus,  in  the  cetacea  this  organ  ascends  as  far  as  the  posterior 
nares,  and  communicates  with  the  spouting  hole,  which  opens  at 
the  top  of  the  head  by  a  single  or  double  orifice,  closed  by  a  fleshy 
valve  in  the  form  of  two  semicircles.  The  great  size  of  the  larynx 
in  the  lion  accounts  for  the  powerful  and  terrific  roar  of  that  ani- 


ORGANS  OF  GENERATION  IN  THE  INVERTEBRATA.  97 

mal.  The  peculiar  grunting  voice  of  the  pig  is  produced  by  large 
lateral  cavities  communicating  with  the  small  ventricles  of  the 
larynx,  and  the  neighing  of  the  horse  results  from  the  vibrations  of 
membranous  folds  connected  with  the  chordae  volcales. 

The  trachea  varies  considerably  in  the  length,  breadth,  and  num- 
ber of  its  rings;  thus,  in  the  seal,  the  porpoise,  the  cheiroptera,  and 
several  rodentia,  its  rings  form  complete  circles  as  in  birds  ;  their 
number  varies  from  14,  presented  by  the  mouse,  to  78,  as  seen  in  the 
seal.  In  the  sloth  the  trachea  descends  considerably  in  the  chest, 
and  again  ascends  to  divide  into  the  bronchi.  The  lungs  present 
very  few  varietes  in  the  class  mammalia.  In  the  cetacea  they 
are  remarkable  for  their  elongated,  flattened  form,  and  for  the  free 
communication  of  their  cells  with  each  other. 


RECAPITULATION. 

1.  The  respiratory  apparatus  is  very  extensive  and  greatly  varied 
in  the  invertebrata,  in  the  lowest  orders  of  which  it  is  usually  con- 
fined to  the  surface  of  the  body. 

2.  Respiration  is  performed  by  gills  in  fishes,  and  in  the  caduci- 
branchiate  amphibia,  during  the  tadpole  state ;  in  the  siren  and 
proteus  it  is  in  all  probability  performed  all  through  life  both  by 
gills  and  lungs. 

3.  In  birds  this  system  is  extended  into  the  bones  and  into  the 
large  cells  of  the  thorax  and  abdomen. 

4.  The  organs  of  respiration  throughout  the  class  mammalia, 
are  very  similar  to  those  of  man. 


CHAPTER  XVII. 

ORGANS  OF  GENERATION  IN  THE  INVERTEBRATA. 

Notwithstanding  the  varied  modifications  observed  in  the  organs 
of  generation  throughout  the  animal  kingdom,  the  reproductive 
function  will  be  found  to  conform  to  a  few  leading  types,  as  the 
fissiparous,  sfemmiparons,  oviparous,  viviparous,  and  ovo-vivipa- 
rous.  Fissiparous  generation  consists  in  the  division  of  an  animal 
into  two  or  more,  similar  in  every  respect  to  the  original  being.  In 
this  form  of  generation,  which  is  met  with  in  some  of  the  infusoria, 
cestoidea,  and  annelida.  the  line  of  separation  takes  different  direc- 
tions, being  transverse  in  the  paramoecuim,  and  vertical  in  the  vor- 
ticellae.  In  gemmiparous  generation  the  young  appear  as  sprouts 
from  the  body  of  the  parent:  it  is  more  extended  than  the  last, 
being  met  with  in  the  polypine  and  coralline  animals,  in  sponges, 
cystiform  entozoa,  and  in  some  acalephae.  These  two  forms  of 
9 — e  evers  7 


98 


EVERS'S  COMPARATIVE  ANATOMY. 


reproduction  appertain  to  animals  unprovided  with  special  organs 
of  generation. 

In  oviparous  generation,  which  belongs  to  birds,  many  reptiles 
and  fishes,  the  egg^  after  fecundation,  passes  through  the  oviduct 
from  the  body  of  the  parent,  to  be  hatched  by  the  influence  of 
external  agents.  Most  mammalia  afford  examples  of  the  viviparous 
form  of  generation,  here  the  ovum  remains  within  the  uterus  of 
of  the  female  until  it  is  capable  of  independent  life.  Many  animals, 
however,  besides  mammalia,  bear  their  young  alive,  examples  of 
which  are  to  be  met  with  among  the  reptiles,  fishes,  mulluscous 
and  articulate  animals.  The  last  form  of  generation  above  alluded 
to  is  the  ovo-viviparous,  which  implies  the  production  of  living 
foetus,  the  ovum  being  hatched  within  the  body  of  the  parent; 
but  never  contracting  a  vascular  connection  with  the  uterus,  this  is 
the  case  with  the  monotremata,  as  the  echidna,  and  ornithorhynchus, 
and  also  with  the  monotrematous  marsupiata,  as  the  opossum,  and 
kangaroo. 

All  the  higher  classes  of  animals  possess  generative  organs  of 
two  kinds,  the  co-operation  of  which,  for  the  purposes  of  reproduc- 
tion, constitutes  the  distinction  of  sex,  into  male  and  female. 

The  following  table  exhibits  a  view  of  the  reproductive  process 
in  the  different  classes  of  animals,  as  given  by  Dr.  Thomson,  of 
Edinburgh,  in  his  matchless  article  on  generation,  in  the  "Cyclo- 
paedia of  Anatomy  and  Physiology." 

f  Parent  splits,  each  part  a  new  ani- 
mal. 
J      1.  Transverse, 
f  Fissiparous  .    .     \      2.  Longitudinal. 
3.  Irregular. 
I  Parent    splits    and    discharges   the 


Non-sexual 


o 

O 

J-H 


youn< 


v  Sexual 


I  r«o™™^o™„„         $  Budding  upon  the  parent  stock. 
^Gemmiparous  .      J  Separatbed  Duds,  gemmae,  or sporules 

1.  On  all  parts  of  the  body. 

2.  On  one  part  or  organ  only. 

f  Hermaphrodite  Both  sexual  organs  on  one  individual. 

1.  Self-impregnation. 

2.  Mutual  impregnation. 
'Oviparous    laying   eggs  which  are 


hatched. 
1.  External  fecundation. 
L  Dioecious      .     .     <{      2.  Internal  fecundation. 

Ovo-viviparous,  eggs  hatched  within 

the  maternal  body. 
.Mammiferous,  suckling  the  young. 

1.  Monotrematous. 

2.  Marsupial. 

3.  Placental  or  strictly  viviparous. 

Prom  the  above  table,  it  appears  that  there  are  a  vast  number  of 
animals  wholly  destitute  of  generative  apparatus,  and  where  organs 
first  appear,  the  animals  seem  to  have  the  power  of  pro*J5agati ng  by 
means  of  ova,  without  copulation ;  in  many  of  the  lower  animals, 


ORGANS  OF  GENERATION  IN  THE  INVERTEBRATA.  99 

however,  as  the  annelida,  the  acephalous,  and  gasteropodous  mol- 
lusca,  both  sets  of  organs  are  placed  on  the  same  individual,  con- 
stituting it  an  hermaphrodite.  Some  of  animals  of  this  class,  as 
the  holothuriae,  possess  the  power  of  self-impregrmtion,  whilst 
others,  though  possessing  double  organs,  require  mutual  impregna- 
tion ;  this  is  the  case  with  the  leech,  and  the  common  earth-worm. 
In  all  the  insect  tribes  the  sexes  are  separate,  the  male  organs  being 
the  testicles,  the  vesiculae  seminales,  the  excretory  tubes,  and  in 
many,  the  prehensores.or  organs  for  seizing  the  female  during 
coitus.  The  female  organs  consist  of  the  ovaria,  the  oviducts,  the 
spermotheca,  or  receptacle  for  the  male  semen,  and  the  ovipositor, 
an  instrument  for  directing  the  ova  to  their  proper  location  at  the 
period  of  extrusion. 

The  generative  system  of  the  arachnida  and  Crustacea  is  very 
simple,  consisting  in  the  male,  of  testes  and  vasa  deferentia,  and  in 
the  female,  of  membranous  ovaries  with  their  excretory  ducts. 
These  organs  are  double  in  each  sex,  and  quite  distinct  from  each 
other. 

In  the  mollusca,  the  generative  organs  present  some  peculiarities; 
there  is  but  one  testicle  in  the  male,  and  one  ovary  in  the  female, 
each  placed  on  the  right  side  of  the  neck.  The  penis  is  of  huge 
dimensions  in  the  gasteropoda,  while  in  the  cephalopoda  it  is  quite 
rudimentary;  but,  by  way  of  compensation,  the  vas  deferens  is 
large,  convoluted,  and  muscular. 

When  two  snails  amorously  disposed,  meet,  as  Professor  Jones, 
of  London,  lucidly  observes,  they  begin  their  blandishments  by 
rubbing  the  surfaces  of  their  bodies  together;  after  some  hours 
the  generative  orifice  on  the  side  of  the  neck  is  seen  to  dilate,  and 
to  display  within  its  cavity  three  apertures,  one  from  the  penis, 
another  from  the  female  organs,  and  the  third  from  the  sac  which 
contains  a  calcareous  quadrangular  spike,  called  the  dart;  the  use 
of  which  seems  to  be  to  excite  to  love  its  sluggish,  sleepy,  apathetic 
associate,  by  pricking  the  surface  of  its  body;  at  length  his  dart  is 
broken,  and  he  becomes  in  turn  the  object  of  a  similar  attack  ;  both 
the  reptile  cupids  having  thus  exhausted  their  quivers,  and  received, 
each,  the  love  inspiring  wound,  the  other  two  orifices  now  dilate, 
from  one  the  Ions:  whip-like  penis  protrudes,  and  is  received  by  the 
vaginal  orifice  of  the  other;  these  phenomena  being  reciprocal,  they 
mutually  embrace  and  impregnate  each  other. 


100 


CHAPTER  XVIII. 

ORGANS  OF  GENERATION  IN  THE  VERTEBRATA. 
PISCES. 

In  this  extensive  class,  the  generative  apparatus  is  comparatively 
simple,  consisting  in  the  female  osseous  family  of  two  large  mem- 
branous ovaries,  with  short  oviducts,  opening  in  the  vicinity  of  the 
anus.  The  ova  are  generally  very  numerous,  and  are  deposited  in 
shallow  water  where  they  receive  the  fecundating  influence  of  the 
male,  and  the  genial  heat  of  the  solar  rays.  In  the  males  the  tes- 
ticles are  of  great  size  and  composed  of  a  congeries  of  convoluted 
tubes;  the  semen  is  discharged  by  the  vasa  deferentia,  and  diffused 
through  the  water  in  the  neighbourhood  of  the  ova,  which  are  thus 
impregnated.  The  presence  of  a  penis  in  this  class  is  not  necessary, 
seeing  that  copulation  does  not  occur;  to  this,  however,  there  are 
a  few  exceptions,  in  which  the  ova  are  fecundated  prior  to  their 
discharge;  and  in  the  blennius  viviparus,  the  young  are  produced 
alive,  being  hatched  within  the  oviduct.  In  these  rare  instances, 
the  vas  deferens  protrudes  externally  in  the  form  of  a  little  penis. 
In  the  eel,  the  lamprey,  and  many  cartilaginous  fishes,  the  ova  are 
suspended  in  the  interior  of  the  abdomen  where  they  receive  the 
influence  of  the  semen,  and  are  discharged  by  a  simple  orifice  near 
the  anus. 

AMPHIBIA. 

The  ovaria  of  these  animals  are  smaller,  but  in  other  respects 
similar  to  those  of  the  lamprey  ;  the  oviducts  are  long  and  tortuous; 
they  commence  by  a  fimbriated  extremity,  and  previous  to  their 
termination  in  the  cloaca  they  enlarge  to  retain  the  ova  for  some 
time  before  expulson.  In  the  frog,  the  testicles,  which  are  two  in 
number,  are  placed  on  the  kidneys,  and  their  excretory  tubes  dis- 
charge themselves  into  the  ureters.  In  the  majority  of  instances, 
the  ova  are  fecundated  in  exitu  by  the  sprinkling  of  the  semen  from 
the  male  which  is  placed  on  the  back  of  his  mate.  In  the  triton, 
and  a  few  others,  the  semen  diffused  through  the  water  passes  into 
the  genital  organs  and  produces  internal  impregnation.  The  sala- 
mander alone  possesses  a  rudimentary  penis,  and  in  this  case,  too, 
the  eggs  are  hatched  within  the  oviduct. 

The  reptilia,  for  the  greater  part,  possess  a  generative  system, 
the  same  as  the  amphibia  ;  the  higher  orders  accomplish  internal 
impregnation.  The  males  of  serpents' are  generally  provided  with 
two  penises  which,  instead  of  being  perforate,  are  grooved  for  the 
passage  of  the  semen  into  the  cloaca  of  the  female.  In  the  sauria 
the  penis  is  bifid,  and  its  extremities  covered  with  recurved  spines. 


ORGANS  OF  GENERATION  IN  THE  VERTEERATA.      101 


AVES. 


In  the  males  of  this  class,  the  testes,  two  in  number,  are  placed 
high  in  the  abdomen,  beneath  the  kidneys;  they  are  subject  to  re- 
markable variation  of  size,  according  to  the  period  of  the  year  their 
office  is  required;  thus,  in  January  the  testicle  of  the  sparrow  is 
about  this  size,  o,  and  by  April  it  attains  the  size  of  a  large  pea. 
The  vasa  deferentia,  seldom  much  curved,  pass  down  and  terminate 
separately  on  a  rudimentary  penis  in  the  urethro-sexual  pouch. 
The  epididymis  is  quite  rudimentary,  and  varies  much  in  colour, 
being  black,  yellow,  or  green.  Coitus  is  usually  effected  simply  by 
an  eversion  of  the  cioacag,  therefore  the  intromittent  organ  is  only 
rudimentary:,  in  those  birds,  however,  which  copulate  in  water,  as 
the  drake,  swan,  &c,  it  necessarily  attains  a  larger  size.  It  is 
sometimes  double  as  in  serpents,  and  is  always  grooved  along  its 
upper  surface,  for  the  passage  of  the  semen.  The  ovarium  and 
oviduct  are  confined  to  the  left  side,  they  primarily,  however,  exist 
on  both  sides,  but  rarely  continue  their  development  on  the  ri<rht. 
A  clitoris  is  present  in  the  females  of  those  species  whose  males°are 
provided  with  a  penis. 


MAMMALIA. 


The  male  organs  of  generation  in  this  class  consist  of  the  testicles, 
vasa  deferentia,  penis,  urethra,  vesiculas  seminales,  the  prostatic 
and  Cowper's  glands,  and  with  one  interesting  exception,  supplied 
by  the  monotremata,  the  genito-urinary  systems  are  quite  distinct 
from  the  digestive.  In  by  far  the  greater  number  of  mammalia  the 
testicles  descend  into  the  scrotum  as  in  man ;  in  some,  however,  as 
the  amphibious  mammalia,  the  cetacea,  the  elephant,  and  the  orni- 
thorhynchus,  they  never  leave  the  abdomen,  and  in  others,  as  the 
bat,  the  mole,  and  the  hedge-hog,  among  the  insectivora;  the  rat, 
the  guinea-pig,  the  porcupine,  and  the  squirrel,  among  the  rodentia, 
they  descend  during  the  rutting  season,  and  return  into  the  abdomen 
after  it  is  over.  The  communication  between  the  tunica  vaginalis 
and  the  peritoneum  remains  unclosed  in  those  animals  in  which  the 
testicles  descend,  except  man,  and  where  these  glands  occasion- 
ally pass  into  and  out  of  the  cavity,  the  communication  is  very 
free.  The  vasa  deferentia  are  very  serpentine  in  those  ani- 
mals where  the  testicles  remain  in  the  abdomen,  and  in  ruminants, 
the  elephant,  and  especially  the  horse,  they  are  greatly  dilated  near 
their  termination  in  the  urethra. 

Vesiculce  Seminales.— There  seems  to  be  no  general  law  for  the 
presence  or  absence  of  these  accessory  bodies.  They  are  met  with 
ID  the  camel,  elephant,  bull,  ram,  horse,  boar,  guinea-pig,  rabbit, 
hedge-hog,  &c.  In  these  animals  they  have  either  no  communica- 
tion, or  a  very  imperfect  one,  with  the  vas  deferens.  In  man  and 
the  simiae  only  is  the  communication  free  and  direct.    The  prostate 


102  EVERs's  COMPARATIVE  ANATOMY. 

is  more  constant  in  its  existence  than  the  vesiculae,  being  found  in 
all  orders  of  the  mammalia,  excepting  perhaps  the  greater  number 
of  the  rodentia  and  insectivora.  It  is  double  in  the  elephant,  the 
camel,  the  horse,  and  some  others.  Compels  glands,  which  are 
small,  and  situate  behind  the  bulb  of  the  urethra  in  the  human 
subject,  are  large,  and  often  increased  in  number  in  other  animals, 
thus  in  the  opossum  and  kangaroo-rat  there  are  four,  and  in  the 
wombat,  kangaroo,  and  others,  as  many  as  six.  They  are  absent 
from  the  greater  number  of  carnivora,  ruminantia,  and  cetacea.  In 
the  marsupiata  they  are  covered  by  a  strong  muscular  stratum,  and 
in  the  icheneumon,  their  ducts  run  forward,  and  open  near  the 
extremity  of  the  penis. 

Penis. — This  organ  is  modified  considerably  throughout  the 
class.  Thus,  in  the  digitigrade  carnivora,  as  the  dog  and  the  lion,  its 
two  crura  are  separated  by  a  distinct  fibrous  septum,  which  is  absent 
in  the  cetacea,  pachydermata,  and  plantigrade  carnivora.  In  the 
cheiroptera,  qnadrumana,  cetacea,  rodentia,  and  carnivora,  with  the 
exception  of  the  hyena,  and  a  few  others,  the  penis  is  occupied  by 
a  cylindrical  bone  occasionally  grooved.  Remarkable  peculiarities 
exist  in  the  intromittent  organ  of  the  marsupiata;  in  the  opossum 
the  glans  is  bifid,  and  has  three  openings,  one  for  the  urine,  and 
two  for  the  semen.  In  the  ornithorhynchus  paradoxus  the  penis  is 
double  anteriorly,  and  in  the  hystrix,  it  divides  into  four  glands, 
each  furnished  with  sharp  papillse  perforated  for  the  discharge  of 
the  semen,  but  in  neither  of  these  strangely  organised  animals  does 
the  urine  pass  through  it,  this  organ  being  concealed  within  the 
cloaca.  The  urethra  shall  be  deferred  till  the  consideration  of  the 
urinary  organs. 

The  female  organs  of  generation  in  the  mammalia  consist  of  the 
vulva,  clitoris,  nymphse,  vagina,  uterus,  Fallopian  tubes,  and  ovaries. 
These  latter  organs  are  invariably  double;  in  the  marsupiata 
their  structure  is  racemose  as  in  birds,  but  in  all  the  other  genera 
they  are  more  solid,  and  approach  more  or  less  the  human  type. 
The  Fallopian  tubes  present  but  few  peculiarities,  except  in  the 
echidna  and  ornithorhynchi,  where  they  experience  a  dilatation  in- 
feriorly  to  supply  the  place  of  a  uterus,  and  afterwards  open  sepa- 
rately into  the  short  vagina,  on  each  side  of  the  orifice  of  the  urin- 
ary bladder.  In  the  lower  orders  of  mammalia  the  urethral  and 
sexual  passages  are  blended  together,  the  uterus  is  elongated  in  form, 
and  thin  in  its  walls;  in  the  carnivora,  ruminantia,  pachydermata, 
and  cetacea,  a  mesial  cleft  appears,  and  the  cornua  are  greatly  deve- 
loped ;  and  in  the  marsupiata  and  most  rodentia,  the  organ  is 
divided  into  two  lateral  halves,  each  opening  separately  into  the 
vagina,  which,  in  the  virgin  state  of  the  sloth,  the  ass,  the  mare, 
the  pig,  and  the  cow,  is  divided  by  a  narrow  ve3itical  septum.  The 
external  organs  of  generation  afford  no  striking  peculiarities,  except 
in  the  deficiency  of  nymphae  and  hymen. 

From  a  review  of  the  above  details  of  the  generative  organs  in 
the  marsupial  and  monotrematous  orders,  one  must  expect  to  find 


ORGANS  OF  GENERATION  IN  THE  VERTEBRATA.      103 

some  peculiarity  in  their  mode  of  generation.  In  all  the  other 
mammalia  the  ovum  is  fecundated  in  the  ovary,  from  which  it  de- 
scends through  the  Fallopian  tube  to  the  uterus,  in  the  higher 
orders  about  the  twelfth  day.  An  intimate  vascular  connection  is 
now  established  between  the  ovum  and  the  uterus,  by  means  of  the 
placenta,  and  continues  till  the  embryo  is  fully  formed,  and  as  we 
say,  capable  of  enjoying  an  independent  existence.  This  consti- 
tutes the  period  of  utero-gestation,  which,  in  the  human  subject  is 
ten  lunar  months,  but  varies  in  almost  every  species  of  the  class. 
A  very  different  process,  however,  takes  place  in  the  animals  above 
alluded  to,  thus  in  the  kangaroo,  the  foetus,  small  and  imperfect, 
leaves  the  uterus  about  the  thirty-ninth  day  after  conception,  and 
is  lodged  by  the  mother  in  the  marsupium  or  pouch  formed  for  its 
reception  on  the  lower  part  of  the  abdomen,  by  a  fold  of  integument 
in  which  the  mammary  gland  is  placed.  Shortly  after  it  reaches 
the  pouch,  it  is  found  attached  by  its  mouth  to  one  of  the  nipples, 
from  which  it  receives  a  constant  supply  of  milk ;  this  is  rendered 
more  secure  by  the  gland  being  covered  over  by  a  stratum  of  mus- 
cular fibres,  which  enables  the  mother  to  feed  the  foetus  at  pleasure. 

The  mode  of  breeding  of  the  monotremaia  is  as  yet  involved  in 
some  obscurity.  The  word  monotremata  means  animals  with  a 
single  outlet  from  the  genito-urinary  and  digestive  organs,  called  a 
cloaca;  and  is  applicable  to  all  the  marsupiata,  but  is  at  present 
confined  to  the  edentate  species  of  them,  as  the  echidna  and  orni- 
thorhynchi.  Previous  to  the  late  valuable  researches  of  Mr.  Owen, 
the  existence  of  mammary  glands  in  these  animals  was  denied, 
which,  combined  with  the  structure  of  their  ovaries,  and  their  pe- 
culiar development  of  uterus,  led  to  the  supposition  of  their  being 
oviparous  in  their  generation. 

Although  the  structure  of  their  generative  organs,  the  presence 
of  mammary  glands,  their  bearing  their  young  alive,  and  suckling 
them,  confer  on  them  the  ovo-viviparous  type  of  generation,  it  must 
be  acknowledged  they  possess  many  characters  in  common  with 
reptiles. 


RECAPITULATION. 

1.  All  forms  of  generation  conform  to  the  fissiparous,  gemmipa- 
rous,  oviparous,  viviparous,  and  ovo-viviparous. 

2.  These  organs  are  separate  and  distinct  in  the  insecta,  the 
annelida,  and  the  Crustacea.  In  the  mollusca  they  are  single,  and 
confined  to  one  side. 

3.  This  system  is  simple  in  fishes,  and  a  rudimentary  penis  oc- 
casionally present. 

4.  Internal  impregnation  rarely  occurs  among  the  amphibia  or 
reptiles. 

5.  In  birds  the  size  of  the  testicles  varies  according  to  the  season, 
and  the  penis  is  often  absent. 


104 

6.  In  some  orders  of  mammalia  the  testicles  never  leave  the 
abdomen,  and  in  others  they  descend  at  certain  periods. 

7.  There  is  no  general  law  for  the  presence  or  absence  of  vesi- 
culae  seminales  or  prostate,  the  latter  is  more  generally  present . 

8.  The  penis  in  many  instances  is  furnished  with  a  bone ;  in 
some  it  is  bifid,  and  in  the  ornithorhynchus  no  urine  passes 
through  it. 

9.  The  generative  organs  and  mode  of  generation  are  peculiar 
in  the  monotremata. 


CHAPTER  XIX. 

URINARY  ORGANS  IN  THE  INVERTEBRATA. 

The  urinary,  like  the  biliary  and  lachrymal  apparatus,  consists 
of  four  principal  parts,  each  having  its  peculiar  office  consigned  to 
it,  and  all  jointly  contributing  to  the  same  end — namely,  the  sepa- 
ration from  the  blood,  and  the  discharge  from  the  system,  of  certain 
decomposed  and  effete  animal  and  saline  matters.  The  urinary 
organs,  when  complete,  as  they  are  in  the  higher  orders  of  animals 
consist  of  the  kidneys,  the  ureters,  the  bladder,  and  the  urethra. 

Although  the  mollusca  secrete  urine,  and  uric  acid  has  been  de- 
tected in  the  long  convoluted  caeca  of  insects,  and  even  through 
the  bodies  of  cantharides  ;  yet  no  perfect  urinary  system  has  been 
discovered  in  the  great  invertebrate  division  of  animals.  It  is  more 
than  probable  that  the  function  of  the  kidneys  in  the  majority  of 
instances  devolves  on  the  respiratory,  the  cutaneous,  and  the  biliary 
systems,  together  with  certain  glands,  many  of  which  serve  not  only 
for  the  elimination  of  noxious  materials  from  the  system,  but  as  or- 
gans of  defence  on  the  approach  of  danger;  in  this  latter  light  may 
be  regarded  the  acrid  secretions  of  bees,  beetles,  wasps,  and  spiders  ; 
as  also  the  ink  of  the  cuttle-fish  which  has  the  effect  of  blackening 
a  considerable  extent  of  the  surrounding  water,  and  thus  baffling 
the  attacks  of  its  enemies :  and  among  the  vertebrata,  a  striking 
example  is  presented  by  the  yagouare  of  Azara,  one  of  the  mephitic 
weasels  of  Chili,  whose  urine  is  rendered  so  intensely  offensive  by 
the  secretion  of  some  adjoining  glands,  that  dogs  or  other  animals 
which  have  been  sprinkled  with  it  during  their  pursuit  of  this  crea- 
ture, are  said  to  have  torn  portions  of  their  own  skins  off  from  dis- 
gust, notwithstanding  careful  and  repeated  ablutions. 


URINARY  ORGANS  IN  THE  VERTEBRATA.  105 

CHAPTER  XX. 

URINARY  ORGANS  IN  THE  VERTEBRATA. 
PISCES. 

The  kidneys  in  this  class  are  long  and  narrow,  sometimes  extend- 
ing the  whole  length  of  the  abdomen,  as  in  the  burbot.  They 
generally  present  the  appearance  of  forming  but  a  single  mass, 
their  separation  being  only  indicated  by  the  presence  of  the  ureters 
and  the  cava.  The  ureters,  which  arise  by  numerous  fine  radicles, 
soon  unite  in  all  the  osseous  fishes,  into  a  single  tube,  which  forms 
a  heart  shaped  dilatation  previous  to  its  termination  behind  the 
anus,  in  common  with  the  sexual  organs. 

Bladder. — This  reservoir  is  absent  from  all  the  osseous,  and 
several  of  the  cartilaginous  fishes,  as  the  ray  and  shark,  in  which 
the  ureters  open  as  in  birds,  into  a  cloaca:  when  it  is  present  as  in 
the  lump-fish,  it  receives  the  ureters  anteriorly,  and  opens  behind 
the  anus  in  common  with  the  vasa  deferentia. 

H 

AMPHIBIA. 

The  kidneys  are  more  distinct  in  this  class  than  in  fish.  They 
are  greatly  lengthened  in  the  aquatic  genera,  but  are  much  shorter  in 
the  frog.  The  ureters  convey  the  urine  to  the  bladder,  which  is 
situated  in  front  of  the  rectum  :  in  the  frog  it  is  of  considerable  size, 
its  walls  are  thin,  and  its  fundus  presents' two  cornua.  In  the  rep- 
tilia  the  kidneys  afford  but  few  peculiarities,  being  elongated  in  the 
lizard,  as  in  fish,  and  somewhat  oval  in  the  tortoise.  The  ureters 
are  longer  in  this  class  than  in  the  amphibia,  and  discharge  them- 
selves either  into  the  cloaca  or  bladder.  This  organ  is  absent  from 
the  ophidia,  and  several  of  the  sauria,  as  the  lizard,  and  the  croco- 
dile. It  is  very  large  in  the  chelonia,  as  the  tortoise,  and  it  is  sin- 
gular, that  the  ureters  instead  of  going  to  it,  empty  themselves  into 
the  urethra  in  front  of  it,  so  that  the  urine  has  to  re-ascend  to  the 
urinary  reservoir. 

AVES. 

In  this  extensive  oviparous  class  the  kidneys  are  of  great  length, 
extending  along  the  spine,  from  the  lungs  to  the  lower  end  of  the 
rectum.  These  organs  are  relatively  larger  in  birds  than  in  the 
terrestrial  mammalia — a  circumstance  which  is  explained  by  recol- 
lecting the  nature  of  their  integuments,  and  the  little  transposition 
they  admit  of.  They  are  of  small  size  in  the  bustard  and  heron, 
and  their  lower  extremities  are  somewhat  blended  together  in  the 
coot.  Their  structure  is  remarkable  for  the  absence  of  cortical 
portion  ;  the  tubuli  uriniferi  run  to  the  surface,  and  by  their  con- 


106- 

fluence  form  the  commencement  of  the  ureter,  which  descends 
along  the  surface  of  the  kidney,  and  posterior  wall  of  the  rectum, 
and  terminates  in  that  part  of  the  cloaca  called  the  urethro-sexual 
cavity.  The  space  between  their  termination  and  that  of  the  rec- 
tum is  large  in  the  owl  and  many  aquatic  birds,  and  is  looked  upon 
by  some  as  a  rudiment  of  urinary  bladder. 

The  supra-renal  capsules  are  small,  of  a  bright  yellow  colour, 
and  placed  on  the  inner  and  upper  part  of  each  kidney,  in  contact 
with  the  testicle  or  the  ovary.  They  are  erroneously  supposed  by 
some  to  have  some  functional  relation  to  the  generative  system. 

MAMMALIA. 

The  kidneys  are  lobulated  in  the  cetacea,  seals,  otters,  bears,  the 
elephant,  the  ox,  &c,  as  in  the  human  foetus.  In  the  otter  each 
kidney  consists  of  about  ten  lobules;  in  the  bear  of  about  fifty,  and 
in  the  seal  as  many  as  a  hundred  and  thirty.  They  present  a  lobu- 
lated appearance  in  many  other  mammalia  during  the  early  periods 
of  existence.  The  ureters  enter  the  bladder  in  an  oblique  direction, 
a  little  behind  its  neck,  in  all  the  animals  of  this  class,  with  the  ex- 
ception of  the  echidna  and  ornithorhynchus,  in  which  they  open 
into  the  urethra  near  its  commencement,  so  that  the  urine  must  ?G- 
ascend  to  the  bladder,  as  in  the  chelonian  reptiles.  In  the  mamma- 
lia generally  the  bladder  lies  more  loose  in  the  abdomen  than  in 
the  human  subject,  owing  to  its  more  perfect  peritoneal  investment. 
For  the  greater  part  it  is  more  muscular  and  less  capacious  in  the 
carnivora  than  in  the  herbivorous  tribes.  In  the  rodentia,  however, 
it  is  small  and  fleshy.  The  shape  of  the  bladder  will  be  found  to 
vary  in  obedience  to  age,  sex,  and  species,  the  younger  the  animal, 
however,  the  more  elongated  will  it  be  found,  and  in  the  human 
embryo  it  is  cylindrical,  tapering  towards  the  urachus  above,  and 
the  urethra  below. 

The  renal  capsules,  like  the  kidneys,  are  lobulated  in  the  cetacea, 
and  other  aquatic  mammalia,  and  are  found  relatively  very  large 
in  the  young  of  animals  possessing  them.  The  urethra,  as  in  the 
human  subject,  consists  of  a  membranous  or  muscular,  and  of  a 
spongy  portion,  the  former  receiving  the  accessory  secretions.  In 
the  boar  and  many  ruminants  these  two  portions  join  at  an  angle. 
The  corpus  spongiosum  arises  by  two  roots  in  most  of  the  marsu- 
piata,  and  in  the  kangaroo,  the  urethra  runs  through  the  centre  of 
the  penis  to  its  extremity. 

RECAPITULATION. 

1.  In  the  great  invertebrate  division  of  animals,  the  functions  of 
the  kidneys  seem  to  be  performed  by  other  parts,  as  the  surface  of 
the  body  generally,  and  certain  glands. 

2.  Kidneys  exist  in  all  fishes,  but  a  urinary  bladder  is  confined 
to  the  cartilaginous  tribes. 


NAMES  OF  AUTHORS  CONSULTED.  107 

3.  Birds  have  kidneys  and  supra-renal  bodies,  but  no  bladder. 

4.  The  kidneys  are  lobulated  in  the  adult  state  of  many,  and  in 
the  foetal  state  of  most  mammalia. 

5.  The  ureters  open   into   the   bladder   in   all   the   mammalia, 
excepting  the  monotremata. 


LIST 
OF  THE  PRINCIPAL  AUTHORS  CONSULTED. 

Baron   Cdvier.— Leeons    D'Anatoraie    Comparee— Regne   Animal— Bv 

Griffith,  &c. 
Linnjeus. — Systema  Naturae. 
Grant. — Outlines  of  Comparative  Anatomy,  &c. 
Lamark.— Histoire  Naturelle  des  Animaux  sans  Vertebres. 
Owen.— Clycopaedia  of  Anatomy  and  Physiology,  &c. 
Coldstream. 
Edwards. 

Lawrence. — Zoological  Lectures. 
Bell. — Cyclopaedia  of  Anatomy  and  Physiology. 
Auduin. 
Todd. 
Sir  C.  Bell.— Mechanism  of  the  Human  Hand— Bridgewater  Treatise. 
Blumenbach. — Comparative  Anatomy,  by  Lawrence. 
Deshayes.— Cyclopaedia  of  Anatomy  and  Physiology. 
Harrison. 
Sharpey. 
Carus  by  Gore.— Introduction  to  the  Comparative  Anatomy  of 

Animals. 
F.  Cuvier.— Histoire  Naturelle  des  Mammiferes. 

Houston.— Descriptive   Catalogue   of   the    preparations    in    the 

Museum. 
Fyfe. — Outlines  of  Comparative  Anatomy. 
Thomson.— Cyclopaedia  of  Anatomy  and  Physiology. 
Jacob. 
Jones. 
Sir  E.  Home.— Lectures  on  Comparative  Anatomy. 
Mueller. — Elements  of  Physiology. 
Hunter. — Animal  (Economy. 
Roget—  Bridgewater  Treatise. 
Rees. — Cyclopaedia. 
Blainville.— De    l'Organisation    Des    Animaux,    ou    Principes 

d'Anatomie  Comparee. 


CONTENTS, 


CHAP.  I.  Preliminary  Observations, 

Cuvier's  Classification  of  Animals, 
Grant's  Classification  of  Animals, 
II.  Skeleton  in  the  Invertebrata — General  Remarks, 

III. Vertebrata — General  Observations, 

— Pisces, 

Amphibia, 

Reptilia, 

Aves,  ... 

Mammalia,       ... 

Recapitulation,         - 

Fossil  Bones  of  Animals,  ... 

IV.  Ligamentary  System,  ... 

V.  Muscular  System  in  the  Invertebrata, 
VI. Vertebrata, 


VII. 
VIII. 


Pisces, 

Amphibia, 

Reptilia, 

Aves, 

Mammalia, 

Recapitulation,         - 

Nervous  System  in  the  Invertebrata 

Vertebrata, 

Pisces, 

Amphibia, 

Reptilia, 

Aves, 

Mammalia, 


Recapitulation, 
IX.  Organs  of  Sense — Vision, 

Hearing, 

Smell, 

Taste,     - 

Touch, 

Recapitulation, 
X.  Organs  of  Digestion  in  the  Invertebrata, 


XI. 


Development  of  Teeth, 
Recapitulation, 
XII.  Absorbent  System, 


Vertebrata — Pisces, 

Amphibia, 

Reptilia, 

Aves,  - 

Mammalia, 


PAGE 

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10 
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18 

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22 

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38 

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39 

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42 

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42 

-  43 
44 

-  45 
46 

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48 

-  48 
50 

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51 

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56 

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61 

-  63 
64 

.  65 
65 

.  65 
69 

-  71 
72 

.  73 
76 

-  77 
82 

.    83 


112  CONTENTS. 

XIII.   Sanguiferous  System  in  the  Invertebrata,  84 

XIV. Vertebra  ta— Pisces,          -  -  .86 

Amphibia,      ....  86 

Reptilia,    '  -  -  .87 

. Aves,  ....  88 

Mammalia  .  -  .  89 

Recapitulation,      --,....  91 

XV.  Respiratory  Organs  in  the  Invertebrata,  -  -  -  -       92 

XVI. Vertebrata— Pisces,      ...  94 

Amphibia,  -  -  .  .95 

Reptilia,  -  -  -  95 

Aves,         -  .  .  .  .95 

Mammalia,  ■       .  .  -  96 

Recapitulation,  -  .  -  -  -  -  -       97 

XVII.  Organs  of  Generation  in  the  Invertebrata,  ...  97 

XVIII. Vertebra  I  a— Pisces,        .  -  -     100 

Amphibia,  -  -  100 

Reptilia,  .  -  -  -     100 

Aves,  .  .  .  .101 

. Mammalia,         -  -  .  -     101 

Recapitulation,       -  -  .  ...  .  -  103 

XIX.  Urinary  Organs  in  the  Invertebrata,  ....     104 

XX. Vertebrata— Pisces,  -  -  .  105 

Amphibia,       .....     105 

Reptilia,     -  -  -  -  .105 

Aves,  .  .  .  -  .105 

Mammalia,  .  -  -  .106 

Recapitulation,  .......     106 

Names  of  Authors  who  have  been  consulted,         -  -  -  107 


